diff options
Diffstat (limited to 'Documentation')
29 files changed, 1207 insertions, 555 deletions
diff --git a/Documentation/ABI/testing/debugfs-pktcdvd b/Documentation/ABI/testing/debugfs-pktcdvd index bf9c16b64c3..cf11736acb7 100644 --- a/Documentation/ABI/testing/debugfs-pktcdvd +++ b/Documentation/ABI/testing/debugfs-pktcdvd @@ -1,4 +1,4 @@ -What: /debug/pktcdvd/pktcdvd[0-7] +What: /sys/kernel/debug/pktcdvd/pktcdvd[0-7] Date: Oct. 2006 KernelVersion: 2.6.20 Contact: Thomas Maier <balagi@justmail.de> @@ -10,10 +10,10 @@ debugfs interface The pktcdvd module (packet writing driver) creates these files in debugfs: -/debug/pktcdvd/pktcdvd[0-7]/ +/sys/kernel/debug/pktcdvd/pktcdvd[0-7]/ info (0444) Lots of driver statistics and infos. Example: ------- -cat /debug/pktcdvd/pktcdvd0/info +cat /sys/kernel/debug/pktcdvd/pktcdvd0/info diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index a3a83d38f96..8918a32c6b3 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -31,7 +31,7 @@ PS_METHOD = $(prefer-db2x) ### # The targets that may be used. -PHONY += xmldocs sgmldocs psdocs pdfdocs htmldocs mandocs installmandocs +PHONY += xmldocs sgmldocs psdocs pdfdocs htmldocs mandocs installmandocs cleandocs BOOKS := $(addprefix $(obj)/,$(DOCBOOKS)) xmldocs: $(BOOKS) @@ -213,11 +213,12 @@ silent_gen_xml = : dochelp: @echo ' Linux kernel internal documentation in different formats:' @echo ' htmldocs - HTML' - @echo ' installmandocs - install man pages generated by mandocs' - @echo ' mandocs - man pages' @echo ' pdfdocs - PDF' @echo ' psdocs - Postscript' @echo ' xmldocs - XML DocBook' + @echo ' mandocs - man pages' + @echo ' installmandocs - install man pages generated by mandocs' + @echo ' cleandocs - clean all generated DocBook files' ### # Temporary files left by various tools @@ -235,6 +236,10 @@ clean-files := $(DOCBOOKS) \ clean-dirs := $(patsubst %.xml,%,$(DOCBOOKS)) man +cleandocs: + $(Q)rm -f $(call objectify, $(clean-files)) + $(Q)rm -rf $(call objectify, $(clean-dirs)) + # Declare the contents of the .PHONY variable as phony. We keep that # information in a variable se we can use it in if_changed and friends. diff --git a/Documentation/block/biodoc.txt b/Documentation/block/biodoc.txt index ecad6ee7570..6fab97ea7e6 100644 --- a/Documentation/block/biodoc.txt +++ b/Documentation/block/biodoc.txt @@ -1040,23 +1040,21 @@ Front merges are handled by the binary trees in AS and deadline schedulers. iii. Plugging the queue to batch requests in anticipation of opportunities for merge/sort optimizations -This is just the same as in 2.4 so far, though per-device unplugging -support is anticipated for 2.5. Also with a priority-based i/o scheduler, -such decisions could be based on request priorities. - Plugging is an approach that the current i/o scheduling algorithm resorts to so that it collects up enough requests in the queue to be able to take advantage of the sorting/merging logic in the elevator. If the queue is empty when a request comes in, then it plugs the request queue -(sort of like plugging the bottom of a vessel to get fluid to build up) +(sort of like plugging the bath tub of a vessel to get fluid to build up) till it fills up with a few more requests, before starting to service the requests. This provides an opportunity to merge/sort the requests before passing them down to the device. There are various conditions when the queue is unplugged (to open up the flow again), either through a scheduled task or could be on demand. For example wait_on_buffer sets the unplugging going -(by running tq_disk) so the read gets satisfied soon. So in the read case, -the queue gets explicitly unplugged as part of waiting for completion, -in fact all queues get unplugged as a side-effect. +through sync_buffer() running blk_run_address_space(mapping). Or the caller +can do it explicity through blk_unplug(bdev). So in the read case, +the queue gets explicitly unplugged as part of waiting for completion on that +buffer. For page driven IO, the address space ->sync_page() takes care of +doing the blk_run_address_space(). Aside: This is kind of controversial territory, as it's not clear if plugging is @@ -1067,11 +1065,6 @@ Aside: multi-page bios being queued in one shot, we may not need to wait to merge a big request from the broken up pieces coming by. - Per-queue granularity unplugging (still a Todo) may help reduce some of the - concerns with just a single tq_disk flush approach. Something like - blk_kick_queue() to unplug a specific queue (right away ?) - or optionally, all queues, is in the plan. - 4.4 I/O contexts I/O contexts provide a dynamically allocated per process data area. They may be used in I/O schedulers, and in the block layer (could be used for IO statis, diff --git a/Documentation/cgroups/cpuacct.txt b/Documentation/cgroups/cpuacct.txt index bb775fbe43d..8b930946c52 100644 --- a/Documentation/cgroups/cpuacct.txt +++ b/Documentation/cgroups/cpuacct.txt @@ -30,3 +30,21 @@ The above steps create a new group g1 and move the current shell process (bash) into it. CPU time consumed by this bash and its children can be obtained from g1/cpuacct.usage and the same is accumulated in /cgroups/cpuacct.usage also. + +cpuacct.stat file lists a few statistics which further divide the +CPU time obtained by the cgroup into user and system times. Currently +the following statistics are supported: + +user: Time spent by tasks of the cgroup in user mode. +system: Time spent by tasks of the cgroup in kernel mode. + +user and system are in USER_HZ unit. + +cpuacct controller uses percpu_counter interface to collect user and +system times. This has two side effects: + +- It is theoretically possible to see wrong values for user and system times. + This is because percpu_counter_read() on 32bit systems isn't safe + against concurrent writes. +- It is possible to see slightly outdated values for user and system times + due to the batch processing nature of percpu_counter. diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt index a98a7fe7aab..1a608877b14 100644 --- a/Documentation/cgroups/memory.txt +++ b/Documentation/cgroups/memory.txt @@ -6,15 +6,14 @@ used here with the memory controller that is used in hardware. Salient features -a. Enable control of both RSS (mapped) and Page Cache (unmapped) pages +a. Enable control of Anonymous, Page Cache (mapped and unmapped) and + Swap Cache memory pages. b. The infrastructure allows easy addition of other types of memory to control c. Provides *zero overhead* for non memory controller users d. Provides a double LRU: global memory pressure causes reclaim from the global LRU; a cgroup on hitting a limit, reclaims from the per cgroup LRU -NOTE: Swap Cache (unmapped) is not accounted now. - Benefits and Purpose of the memory controller The memory controller isolates the memory behaviour of a group of tasks @@ -290,34 +289,44 @@ will be charged as a new owner of it. moved to the parent. If you want to avoid that, force_empty will be useful. 5.2 stat file - memory.stat file includes following statistics (now) - cache - # of pages from page-cache and shmem. - rss - # of pages from anonymous memory. - pgpgin - # of event of charging - pgpgout - # of event of uncharging - active_anon - # of pages on active lru of anon, shmem. - inactive_anon - # of pages on active lru of anon, shmem - active_file - # of pages on active lru of file-cache - inactive_file - # of pages on inactive lru of file cache - unevictable - # of pages cannot be reclaimed.(mlocked etc) - - Below is depend on CONFIG_DEBUG_VM. - inactive_ratio - VM internal parameter. (see mm/page_alloc.c) - recent_rotated_anon - VM internal parameter. (see mm/vmscan.c) - recent_rotated_file - VM internal parameter. (see mm/vmscan.c) - recent_scanned_anon - VM internal parameter. (see mm/vmscan.c) - recent_scanned_file - VM internal parameter. (see mm/vmscan.c) - - Memo: + +memory.stat file includes following statistics + +cache - # of bytes of page cache memory. +rss - # of bytes of anonymous and swap cache memory. +pgpgin - # of pages paged in (equivalent to # of charging events). +pgpgout - # of pages paged out (equivalent to # of uncharging events). +active_anon - # of bytes of anonymous and swap cache memory on active + lru list. +inactive_anon - # of bytes of anonymous memory and swap cache memory on + inactive lru list. +active_file - # of bytes of file-backed memory on active lru list. +inactive_file - # of bytes of file-backed memory on inactive lru list. +unevictable - # of bytes of memory that cannot be reclaimed (mlocked etc). + +The following additional stats are dependent on CONFIG_DEBUG_VM. + +inactive_ratio - VM internal parameter. (see mm/page_alloc.c) +recent_rotated_anon - VM internal parameter. (see mm/vmscan.c) +recent_rotated_file - VM internal parameter. (see mm/vmscan.c) +recent_scanned_anon - VM internal parameter. (see mm/vmscan.c) +recent_scanned_file - VM internal parameter. (see mm/vmscan.c) + +Memo: recent_rotated means recent frequency of lru rotation. recent_scanned means recent # of scans to lru. showing for better debug please see the code for meanings. +Note: + Only anonymous and swap cache memory is listed as part of 'rss' stat. + This should not be confused with the true 'resident set size' or the + amount of physical memory used by the cgroup. Per-cgroup rss + accounting is not done yet. 5.3 swappiness Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only. - Following cgroup's swapiness can't be changed. + Following cgroups' swapiness can't be changed. - root cgroup (uses /proc/sys/vm/swappiness). - a cgroup which uses hierarchy and it has child cgroup. - a cgroup which uses hierarchy and not the root of hierarchy. diff --git a/Documentation/cgroups/resource_counter.txt b/Documentation/cgroups/resource_counter.txt index f196ac1d7d2..95b24d766ea 100644 --- a/Documentation/cgroups/resource_counter.txt +++ b/Documentation/cgroups/resource_counter.txt @@ -47,13 +47,18 @@ to work with it. 2. Basic accounting routines - a. void res_counter_init(struct res_counter *rc) + a. void res_counter_init(struct res_counter *rc, + struct res_counter *rc_parent) Initializes the resource counter. As usual, should be the first routine called for a new counter. - b. int res_counter_charge[_locked] - (struct res_counter *rc, unsigned long val) + The struct res_counter *parent can be used to define a hierarchical + child -> parent relationship directly in the res_counter structure, + NULL can be used to define no relationship. + + c. int res_counter_charge(struct res_counter *rc, unsigned long val, + struct res_counter **limit_fail_at) When a resource is about to be allocated it has to be accounted with the appropriate resource counter (controller should determine @@ -67,15 +72,25 @@ to work with it. * if the charging is performed first, then it should be uncharged on error path (if the one is called). - c. void res_counter_uncharge[_locked] + If the charging fails and a hierarchical dependency exists, the + limit_fail_at parameter is set to the particular res_counter element + where the charging failed. + + d. int res_counter_charge_locked + (struct res_counter *rc, unsigned long val) + + The same as res_counter_charge(), but it must not acquire/release the + res_counter->lock internally (it must be called with res_counter->lock + held). + + e. void res_counter_uncharge[_locked] (struct res_counter *rc, unsigned long val) When a resource is released (freed) it should be de-accounted from the resource counter it was accounted to. This is called "uncharging". - The _locked routines imply that the res_counter->lock is taken. - + The _locked routines imply that the res_counter->lock is taken. 2.1 Other accounting routines diff --git a/Documentation/driver-model/platform.txt b/Documentation/driver-model/platform.txt index 83009fdcbbc..2e2c2ea90ce 100644 --- a/Documentation/driver-model/platform.txt +++ b/Documentation/driver-model/platform.txt @@ -169,3 +169,62 @@ three different ways to find such a match: be probed later if another device registers. (Which is OK, since this interface is only for use with non-hotpluggable devices.) + +Early Platform Devices and Drivers +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The early platform interfaces provide platform data to platform device +drivers early on during the system boot. The code is built on top of the +early_param() command line parsing and can be executed very early on. + +Example: "earlyprintk" class early serial console in 6 steps + +1. Registering early platform device data +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The architecture code registers platform device data using the function +early_platform_add_devices(). In the case of early serial console this +should be hardware configuration for the serial port. Devices registered +at this point will later on be matched against early platform drivers. + +2. Parsing kernel command line +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The architecture code calls parse_early_param() to parse the kernel +command line. This will execute all matching early_param() callbacks. +User specified early platform devices will be registered at this point. +For the early serial console case the user can specify port on the +kernel command line as "earlyprintk=serial.0" where "earlyprintk" is +the class string, "serial" is the name of the platfrom driver and +0 is the platform device id. If the id is -1 then the dot and the +id can be omitted. + +3. Installing early platform drivers belonging to a certain class +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The architecture code may optionally force registration of all early +platform drivers belonging to a certain class using the function +early_platform_driver_register_all(). User specified devices from +step 2 have priority over these. This step is omitted by the serial +driver example since the early serial driver code should be disabled +unless the user has specified port on the kernel command line. + +4. Early platform driver registration +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Compiled-in platform drivers making use of early_platform_init() are +automatically registered during step 2 or 3. The serial driver example +should use early_platform_init("earlyprintk", &platform_driver). + +5. Probing of early platform drivers belonging to a certain class +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The architecture code calls early_platform_driver_probe() to match +registered early platform devices associated with a certain class with +registered early platform drivers. Matched devices will get probed(). +This step can be executed at any point during the early boot. As soon +as possible may be good for the serial port case. + +6. Inside the early platform driver probe() +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The driver code needs to take special care during early boot, especially +when it comes to memory allocation and interrupt registration. The code +in the probe() function can use is_early_platform_device() to check if +it is called at early platform device or at the regular platform device +time. The early serial driver performs register_console() at this point. + +For further information, see <linux/platform_device.h>. diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt index 7e2af10e826..de491a3e231 100644 --- a/Documentation/feature-removal-schedule.txt +++ b/Documentation/feature-removal-schedule.txt @@ -428,3 +428,12 @@ Why: In 2.6.27, the semantics of /sys/bus/pci/slots was redefined to After a reasonable transition period, we will remove the legacy fakephp interface. Who: Alex Chiang <achiang@hp.com> + +--------------------------- + +What: i2c-voodoo3 driver +When: October 2009 +Why: Superseded by tdfxfb. I2C/DDC support used to live in a separate + driver but this caused driver conflicts. +Who: Jean Delvare <khali@linux-fr.org> + Krzysztof Helt <krzysztof.h1@wp.pl> diff --git a/Documentation/filesystems/pohmelfs/design_notes.txt b/Documentation/filesystems/pohmelfs/design_notes.txt index 6d6db60d567..dcf83358716 100644 --- a/Documentation/filesystems/pohmelfs/design_notes.txt +++ b/Documentation/filesystems/pohmelfs/design_notes.txt @@ -56,9 +56,10 @@ workloads and can fully utilize the bandwidth to the servers when doing bulk data transfers. POHMELFS clients operate with a working set of servers and are capable of balancing read-only -operations (like lookups or directory listings) between them. +operations (like lookups or directory listings) between them according to IO priorities. Administrators can add or remove servers from the set at run-time via special commands (described -in Documentation/pohmelfs/info.txt file). Writes are replicated to all servers. +in Documentation/pohmelfs/info.txt file). Writes are replicated to all servers, which are connected +with write permission turned on. IO priority and permissions can be changed in run-time. POHMELFS is capable of full data channel encryption and/or strong crypto hashing. One can select any kernel supported cipher, encryption mode, hash type and operation mode diff --git a/Documentation/filesystems/pohmelfs/info.txt b/Documentation/filesystems/pohmelfs/info.txt index 4e3d5015708..db2e4139362 100644 --- a/Documentation/filesystems/pohmelfs/info.txt +++ b/Documentation/filesystems/pohmelfs/info.txt @@ -1,6 +1,8 @@ POHMELFS usage information. -Mount options: +Mount options. +All but index, number of crypto threads and maximum IO size can changed via remount. + idx=%u Each mountpoint is associated with a special index via this option. Administrator can add or remove servers from the given index, so all mounts, @@ -52,16 +54,27 @@ mcache_timeout=%u Usage examples. -Add (or remove if it already exists) server server1.net:1025 into the working set with index $idx +Add server server1.net:1025 into the working set with index $idx with appropriate hash algorithm and key file and cipher algorithm, mode and key file: -$cfg -a server1.net -p 1025 -i $idx -K $hash_key -k $cipher_key +$cfg A add -a server1.net -p 1025 -i $idx -K $hash_key -k $cipher_key Mount filesystem with given index $idx to /mnt mountpoint. Client will connect to all servers specified in the working set via previous command: mount -t pohmel -o idx=$idx q /mnt -One can add or remove servers from working set after mounting too. +Change permissions to read-only (-I 1 option, '-I 2' - write-only, 3 - rw): +$cfg A modify -a server1.net -p 1025 -i $idx -I 1 + +Change IO priority to 123 (node with the highest priority gets read requests). +$cfg A modify -a server1.net -p 1025 -i $idx -P 123 +One can check currect status of all connections in the mountstats file: +# cat /proc/$PID/mountstats +... +device none mounted on /mnt with fstype pohmel +idx addr(:port) socket_type protocol active priority permissions +0 server1.net:1026 1 6 1 250 1 +0 server2.net:1025 1 6 1 123 3 Server installation. diff --git a/Documentation/infiniband/ipoib.txt b/Documentation/infiniband/ipoib.txt index 864ff328378..6d40f00b358 100644 --- a/Documentation/infiniband/ipoib.txt +++ b/Documentation/infiniband/ipoib.txt @@ -24,6 +24,49 @@ Partitions and P_Keys The P_Key for any interface is given by the "pkey" file, and the main interface for a subinterface is in "parent." +Datagram vs Connected modes + + The IPoIB driver supports two modes of operation: datagram and + connected. The mode is set and read through an interface's + /sys/class/net/<intf name>/mode file. + + In datagram mode, the IB UD (Unreliable Datagram) transport is used + and so the interface MTU has is equal to the IB L2 MTU minus the + IPoIB encapsulation header (4 bytes). For example, in a typical IB + fabric with a 2K MTU, the IPoIB MTU will be 2048 - 4 = 2044 bytes. + + In connected mode, the IB RC (Reliable Connected) transport is used. + Connected mode is to takes advantage of the connected nature of the + IB transport and allows an MTU up to the maximal IP packet size of + 64K, which reduces the number of IP packets needed for handling + large UDP datagrams, TCP segments, etc and increases the performance + for large messages. + + In connected mode, the interface's UD QP is still used for multicast + and communication with peers that don't support connected mode. In + this case, RX emulation of ICMP PMTU packets is used to cause the + networking stack to use the smaller UD MTU for these neighbours. + +Stateless offloads + + If the IB HW supports IPoIB stateless offloads, IPoIB advertises + TCP/IP checksum and/or Large Send (LSO) offloading capability to the + network stack. + + Large Receive (LRO) offloading is also implemented and may be turned + on/off using ethtool calls. Currently LRO is supported only for + checksum offload capable devices. + + Stateless offloads are supported only in datagram mode. + +Interrupt moderation + + If the underlying IB device supports CQ event moderation, one can + use ethtool to set interrupt mitigation parameters and thus reduce + the overhead incurred by handling interrupts. The main code path of + IPoIB doesn't use events for TX completion signaling so only RX + moderation is supported. + Debugging Information By compiling the IPoIB driver with CONFIG_INFINIBAND_IPOIB_DEBUG set @@ -55,3 +98,5 @@ References http://ietf.org/rfc/rfc4391.txt IP over InfiniBand (IPoIB) Architecture (RFC 4392) http://ietf.org/rfc/rfc4392.txt + IP over InfiniBand: Connected Mode (RFC 4755) + http://ietf.org/rfc/rfc4755.txt diff --git a/Documentation/input/rotary-encoder.txt b/Documentation/input/rotary-encoder.txt new file mode 100644 index 00000000000..435102a26d9 --- /dev/null +++ b/Documentation/input/rotary-encoder.txt @@ -0,0 +1,101 @@ +rotary-encoder - a generic driver for GPIO connected devices +Daniel Mack <daniel@caiaq.de>, Feb 2009 + +0. Function +----------- + +Rotary encoders are devices which are connected to the CPU or other +peripherals with two wires. The outputs are phase-shifted by 90 degrees +and by triggering on falling and rising edges, the turn direction can +be determined. + +The phase diagram of these two outputs look like this: + + _____ _____ _____ + | | | | | | + Channel A ____| |_____| |_____| |____ + + : : : : : : : : : : : : + __ _____ _____ _____ + | | | | | | | + Channel B |_____| |_____| |_____| |__ + + : : : : : : : : : : : : + Event a b c d a b c d a b c d + + |<-------->| + one step + + +For more information, please see + http://en.wikipedia.org/wiki/Rotary_encoder + + +1. Events / state machine +------------------------- + +a) Rising edge on channel A, channel B in low state + This state is used to recognize a clockwise turn + +b) Rising edge on channel B, channel A in high state + When entering this state, the encoder is put into 'armed' state, + meaning that there it has seen half the way of a one-step transition. + +c) Falling edge on channel A, channel B in high state + This state is used to recognize a counter-clockwise turn + +d) Falling edge on channel B, channel A in low state + Parking position. If the encoder enters this state, a full transition + should have happend, unless it flipped back on half the way. The + 'armed' state tells us about that. + +2. Platform requirements +------------------------ + +As there is no hardware dependent call in this driver, the platform it is +used with must support gpiolib. Another requirement is that IRQs must be +able to fire on both edges. + + +3. Board integration +-------------------- + +To use this driver in your system, register a platform_device with the +name 'rotary-encoder' and associate the IRQs and some specific platform +data with it. + +struct rotary_encoder_platform_data is declared in +include/linux/rotary-encoder.h and needs to be filled with the number of +steps the encoder has and can carry information about externally inverted +signals (because of used invertig buffer or other reasons). + +Because GPIO to IRQ mapping is platform specific, this information must +be given in seperately to the driver. See the example below. + +---------<snip>--------- + +/* board support file example */ + +#include <linux/input.h> +#include <linux/rotary_encoder.h> + +#define GPIO_ROTARY_A 1 +#define GPIO_ROTARY_B 2 + +static struct rotary_encoder_platform_data my_rotary_encoder_info = { + .steps = 24, + .axis = ABS_X, + .gpio_a = GPIO_ROTARY_A, + .gpio_b = GPIO_ROTARY_B, + .inverted_a = 0, + .inverted_b = 0, +}; + +static struct platform_device rotary_encoder_device = { + .name = "rotary-encoder", + .id = 0, + .dev = { + .platform_data = &my_rotary_encoder_info, + } +}; + diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt index 51104f9194a..d76cfd8712e 100644 --- a/Documentation/kbuild/makefiles.txt +++ b/Documentation/kbuild/makefiles.txt @@ -40,10 +40,16 @@ This document describes the Linux kernel Makefiles. --- 6.7 Custom kbuild commands --- 6.8 Preprocessing linker scripts - === 7 Kbuild Variables - === 8 Makefile language - === 9 Credits - === 10 TODO + === 7 Kbuild syntax for exported headers + --- 7.1 header-y + --- 7.2 objhdr-y + --- 7.3 destination-y + --- 7.4 unifdef-y (deprecated) + + === 8 Kbuild Variables + === 9 Makefile language + === 10 Credits + === 11 TODO === 1 Overview @@ -310,6 +316,16 @@ more details, with real examples. #arch/m68k/fpsp040/Makefile ldflags-y := -x + subdir-ccflags-y, subdir-asflags-y + The two flags listed above are similar to ccflags-y and as-falgs-y. + The difference is that the subdir- variants has effect for the kbuild + file where tey are present and all subdirectories. + Options specified using subdir-* are added to the commandline before + the options specified using the non-subdir variants. + + Example: + subdir-ccflags-y := -Werror + CFLAGS_$@, AFLAGS_$@ CFLAGS_$@ and AFLAGS_$@ only apply to commands in current @@ -1143,8 +1159,69 @@ When kbuild executes, the following steps are followed (roughly): The kbuild infrastructure for *lds file are used in several architecture-specific files. +=== 7 Kbuild syntax for exported headers + +The kernel include a set of headers that is exported to userspace. +Many headers can be exported as-is but other headers requires a +minimal pre-processing before they are ready for user-space. +The pre-processing does: +- drop kernel specific annotations +- drop include of compiler.h +- drop all sections that is kernel internat (guarded by ifdef __KERNEL__) + +Each relevant directory contain a file name "Kbuild" which specify the +headers to be exported. +See subsequent chapter for the syntax of the Kbuild file. + + --- 7.1 header-y + + header-y specify header files to be exported. + + Example: + #include/linux/Kbuild + header-y += usb/ + header-y += aio_abi.h + + The convention is to list one file per line and + preferably in alphabetic order. + + header-y also specify which subdirectories to visit. + A subdirectory is identified by a trailing '/' which + can be seen in the example above for the usb subdirectory. + + Subdirectories are visited before their parent directories. + + --- 7.2 objhdr-y + + objhdr-y specifies generated files to be exported. + Generated files are special as they need to be looked + up in another directory when doing 'make O=...' builds. + + Example: + #include/linux/Kbuild + objhdr-y += version.h + + --- 7.3 destination-y + + When an architecture have a set of exported headers that needs to be + exported to a different directory destination-y is used. + destination-y specify the destination directory for all exported + headers in the file where it is present. + + Example: + #arch/xtensa/platforms/s6105/include/platform/Kbuild + destination-y := include/linux + + In the example above all exported headers in the Kbuild file + will be located in the directory "include/linux" when exported. + + + --- 7.4 unifdef-y (deprecated) + + unifdef-y is deprecated. A direct replacement is header-y. + -=== 7 Kbuild Variables +=== 8 Kbuild Variables The top Makefile exports the following variables: @@ -1206,7 +1283,7 @@ The top Makefile exports the following variables: INSTALL_MOD_STRIP will used as the option(s) to the strip command. -=== 8 Makefile language +=== 9 Makefile language The kernel Makefiles are designed to be run with GNU Make. The Makefiles use only the documented features of GNU Make, but they do use many @@ -1225,14 +1302,14 @@ time the left-hand side is used. There are some cases where "=" is appropriate. Usually, though, ":=" is the right choice. -=== 9 Credits +=== 10 Credits Original version made by Michael Elizabeth Chastain, <mailto:mec@shout.net> Updates by Kai Germaschewski <kai@tp1.ruhr-uni-bochum.de> Updates by Sam Ravnborg <sam@ravnborg.org> Language QA by Jan Engelhardt <jengelh@gmx.de> -=== 10 TODO +=== 11 TODO - Describe how kbuild supports shipped files with _shipped. - Generating offset header files. diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 9e4fe724c87..90b3924071b 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -231,6 +231,35 @@ and is between 256 and 4096 characters. It is defined in the file power state again in power transition. 1 : disable the power state check + acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode + Format: { level | edge | high | low } + + acpi_serialize [HW,ACPI] force serialization of AML methods + + acpi_skip_timer_override [HW,ACPI] + Recognize and ignore IRQ0/pin2 Interrupt Override. + For broken nForce2 BIOS resulting in XT-PIC timer. + + acpi_sleep= [HW,ACPI] Sleep options + Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, + old_ordering, s4_nonvs } + See Documentation/power/video.txt for information on + s3_bios and s3_mode. + s3_beep is for debugging; it makes the PC's speaker beep + as soon as the kernel's real-mode entry point is called. + s4_nohwsig prevents ACPI hardware signature from being + used during resume from hibernation. + old_ordering causes the ACPI 1.0 ordering of the _PTS + control method, with respect to putting devices into + low power states, to be enforced (the ACPI 2.0 ordering + of _PTS is used by default). + s4_nonvs prevents the kernel from saving/restoring the + ACPI NVS memory during hibernation. + + acpi_use_timer_override [HW,ACPI] + Use timer override. For some broken Nvidia NF5 boards + that require a timer override, but don't have HPET + acpi_enforce_resources= [ACPI] { strict | lax | no } Check for resource conflicts between native drivers @@ -250,6 +279,9 @@ and is between 256 and 4096 characters. It is defined in the file ad1848= [HW,OSS] Format: <io>,<irq>,<dma>,<dma2>,<type> + add_efi_memmap [EFI; X86] Include EFI memory map in + kernel's map of available physical RAM. + advansys= [HW,SCSI] See header of drivers/scsi/advansys.c. @@ -1840,6 +1872,12 @@ and is between 256 and 4096 characters. It is defined in the file autoconfiguration. Ranges are in pairs (memory base and size). + ports= [IP_VS_FTP] IPVS ftp helper module + Default is 21. + Up to 8 (IP_VS_APP_MAX_PORTS) ports + may be specified. + Format: <port>,<port>.... + print-fatal-signals= [KNL] debug: print fatal signals print-fatal-signals=1: print segfault info to diff --git a/Documentation/lguest/.gitignore b/Documentation/lguest/.gitignore new file mode 100644 index 00000000000..115587fd5f6 --- /dev/null +++ b/Documentation/lguest/.gitignore @@ -0,0 +1 @@ +lguest diff --git a/Documentation/lguest/lguest.txt b/Documentation/lguest/lguest.txt index 29510dc5151..28c747362f9 100644 --- a/Documentation/lguest/lguest.txt +++ b/Documentation/lguest/lguest.txt @@ -3,11 +3,11 @@ /, /` - or, A Young Coder's Illustrated Hypervisor \\"--\\ http://lguest.ozlabs.org -Lguest is designed to be a minimal hypervisor for the Linux kernel, for -Linux developers and users to experiment with virtualization with the -minimum of complexity. Nonetheless, it should have sufficient -features to make it useful for specific tasks, and, of course, you are -encouraged to fork and enhance it (see drivers/lguest/README). +Lguest is designed to be a minimal 32-bit x86 hypervisor for the Linux kernel, +for Linux developers and users to experiment with virtualization with the +minimum of complexity. Nonetheless, it should have sufficient features to +make it useful for specific tasks, and, of course, you are encouraged to fork +and enhance it (see drivers/lguest/README). Features: @@ -37,6 +37,7 @@ Running Lguest: "Paravirtualized guest support" = Y "Lguest guest support" = Y "High Memory Support" = off/4GB + "PAE (Physical Address Extension) Support" = N "Alignment value to which kernel should be aligned" = 0x100000 (CONFIG_PARAVIRT=y, CONFIG_LGUEST_GUEST=y, CONFIG_HIGHMEM64G=n and CONFIG_PHYSICAL_ALIGN=0x100000) diff --git a/Documentation/networking/bonding.txt b/Documentation/networking/bonding.txt index 5ede7473b42..08762750f12 100644 --- a/Documentation/networking/bonding.txt +++ b/Documentation/networking/bonding.txt @@ -1242,7 +1242,7 @@ monitoring is enabled, and vice-versa. To add ARP targets: # echo +192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target # echo +192.168.0.101 > /sys/class/net/bond0/bonding/arp_ip_target - NOTE: up to 10 target addresses may be specified. + NOTE: up to 16 target addresses may be specified. To remove an ARP target: # echo -192.168.0.100 > /sys/class/net/bond0/bonding/arp_ip_target diff --git a/Documentation/powerpc/dts-bindings/fsl/i2c.txt b/Documentation/powerpc/dts-bindings/fsl/i2c.txt index d0ab33e21fe..b6d2e21474f 100644 --- a/Documentation/powerpc/dts-bindings/fsl/i2c.txt +++ b/Documentation/powerpc/dts-bindings/fsl/i2c.txt @@ -7,8 +7,10 @@ Required properties : Recommended properties : - - compatible : Should be "fsl-i2c" for parts compatible with - Freescale I2C specifications. + - compatible : compatibility list with 2 entries, the first should + be "fsl,CHIP-i2c" where CHIP is the name of a compatible processor, + e.g. mpc8313, mpc8543, mpc8544, mpc5200 or mpc5200b. The second one + should be "fsl-i2c". - interrupts : <a b> where a is the interrupt number and b is a field that represents an encoding of the sense and level information for the interrupt. This should be encoded based on @@ -16,17 +18,31 @@ Recommended properties : controller you have. - interrupt-parent : the phandle for the interrupt controller that services interrupts for this device. - - dfsrr : boolean; if defined, indicates that this I2C device has - a digital filter sampling rate register - - fsl5200-clocking : boolean; if defined, indicated that this device - uses the FSL 5200 clocking mechanism. - -Example : - i2c@3000 { - interrupt-parent = <40000>; - interrupts = <1b 3>; - reg = <3000 18>; - device_type = "i2c"; - compatible = "fsl-i2c"; - dfsrr; + - fsl,preserve-clocking : boolean; if defined, the clock settings + from the bootloader are preserved (not touched). + - clock-frequency : desired I2C bus clock frequency in Hz. + +Examples : + + i2c@3d00 { + #address-cells = <1>; + #size-cells = <0>; + compatible = "fsl,mpc5200b-i2c","fsl,mpc5200-i2c","fsl-i2c"; + cell-index = <0>; + reg = <0x3d00 0x40>; + interrupts = <2 15 0>; + interrupt-parent = <&mpc5200_pic>; + fsl,preserve-clocking; }; + + i2c@3100 { + #address-cells = <1>; + #size-cells = <0>; + cell-index = <1>; + compatible = "fsl,mpc8544-i2c", "fsl-i2c"; + reg = <0x3100 0x100>; + interrupts = <43 2>; + interrupt-parent = <&mpic>; + clock-frequency = <400000>; + }; + diff --git a/Documentation/sound/alsa/HD-Audio.txt b/Documentation/sound/alsa/HD-Audio.txt index c5948f2f9a2..88b7433d2f1 100644 --- a/Documentation/sound/alsa/HD-Audio.txt +++ b/Documentation/sound/alsa/HD-Audio.txt @@ -169,7 +169,7 @@ PCI SSID look-up. What `model` option values are available depends on the codec chip. Check your codec chip from the codec proc file (see "Codec Proc-File" section below). It will show the vendor/product name of your codec -chip. Then, see Documentation/sound/alsa/HD-Audio-Modelstxt file, +chip. Then, see Documentation/sound/alsa/HD-Audio-Models.txt file, the section of HD-audio driver. You can find a list of codecs and `model` options belonging to each codec. For example, for Realtek ALC262 codec chip, pass `model=ultra` for devices that are compatible @@ -177,7 +177,7 @@ with Samsung Q1 Ultra. Thus, the first thing you can do for any brand-new, unsupported and non-working HD-audio hardware is to check HD-audio codec and several -different `model` option values. If you have a luck, some of them +different `model` option values. If you have any luck, some of them might suit with your device well. Some codecs such as ALC880 have a special model option `model=test`. diff --git a/Documentation/sparse.txt b/Documentation/sparse.txt index 42f43fa59f2..34c76a55bc0 100644 --- a/Documentation/sparse.txt +++ b/Documentation/sparse.txt @@ -42,6 +42,14 @@ sure that bitwise types don't get mixed up (little-endian vs big-endian vs cpu-endian vs whatever), and there the constant "0" really _is_ special. +__bitwise__ - to be used for relatively compact stuff (gfp_t, etc.) that +is mostly warning-free and is supposed to stay that way. Warnings will +be generated without __CHECK_ENDIAN__. + +__bitwise - noisy stuff; in particular, __le*/__be* are that. We really +don't want to drown in noise unless we'd explicitly asked for it. + + Getting sparse ~~~~~~~~~~~~~~ diff --git a/Documentation/sysctl/net.txt b/Documentation/sysctl/net.txt index a34d55b6544..df38ef046f8 100644 --- a/Documentation/sysctl/net.txt +++ b/Documentation/sysctl/net.txt @@ -95,7 +95,7 @@ of struct cmsghdr structures with appended data. There is only one file in this directory. unix_dgram_qlen limits the max number of datagrams queued in Unix domain -socket's buffer. It will not take effect unless PF_UNIX flag is spicified. +socket's buffer. It will not take effect unless PF_UNIX flag is specified. 3. /proc/sys/net/ipv4 - IPV4 settings diff --git a/Documentation/tomoyo.txt b/Documentation/tomoyo.txt new file mode 100644 index 00000000000..b3a232cae7f --- /dev/null +++ b/Documentation/tomoyo.txt @@ -0,0 +1,55 @@ +--- What is TOMOYO? --- + +TOMOYO is a name-based MAC extension (LSM module) for the Linux kernel. + +LiveCD-based tutorials are available at +http://tomoyo.sourceforge.jp/en/1.6.x/1st-step/ubuntu8.04-live/ +http://tomoyo.sourceforge.jp/en/1.6.x/1st-step/centos5-live/ . +Though these tutorials use non-LSM version of TOMOYO, they are useful for you +to know what TOMOYO is. + +--- How to enable TOMOYO? --- + +Build the kernel with CONFIG_SECURITY_TOMOYO=y and pass "security=tomoyo" on +kernel's command line. + +Please see http://tomoyo.sourceforge.jp/en/2.2.x/ for details. + +--- Where is documentation? --- + +User <-> Kernel interface documentation is available at +http://tomoyo.sourceforge.jp/en/2.2.x/policy-reference.html . + +Materials we prepared for seminars and symposiums are available at +http://sourceforge.jp/projects/tomoyo/docs/?category_id=532&language_id=1 . +Below lists are chosen from three aspects. + +What is TOMOYO? + TOMOYO Linux Overview + http://sourceforge.jp/projects/tomoyo/docs/lca2009-takeda.pdf + TOMOYO Linux: pragmatic and manageable security for Linux + http://sourceforge.jp/projects/tomoyo/docs/freedomhectaipei-tomoyo.pdf + TOMOYO Linux: A Practical Method to Understand and Protect Your Own Linux Box + http://sourceforge.jp/projects/tomoyo/docs/PacSec2007-en-no-demo.pdf + +What can TOMOYO do? + Deep inside TOMOYO Linux + http://sourceforge.jp/projects/tomoyo/docs/lca2009-kumaneko.pdf + The role of "pathname based access control" in security. + http://sourceforge.jp/projects/tomoyo/docs/lfj2008-bof.pdf + +History of TOMOYO? + Realities of Mainlining + http://sourceforge.jp/projects/tomoyo/docs/lfj2008.pdf + +--- What is future plan? --- + +We believe that inode based security and name based security are complementary +and both should be used together. But unfortunately, so far, we cannot enable +multiple LSM modules at the same time. We feel sorry that you have to give up +SELinux/SMACK/AppArmor etc. when you want to use TOMOYO. + +We hope that LSM becomes stackable in future. Meanwhile, you can use non-LSM +version of TOMOYO, available at http://tomoyo.sourceforge.jp/en/1.6.x/ . +LSM version of TOMOYO is a subset of non-LSM version of TOMOYO. We are planning +to port non-LSM version's functionalities to LSM versions. diff --git a/Documentation/ftrace.txt b/Documentation/trace/ftrace.txt index fd9a3e69381..fd9a3e69381 100644 --- a/Documentation/ftrace.txt +++ b/Documentation/trace/ftrace.txt diff --git a/Documentation/vm/kmemtrace.txt b/Documentation/trace/kmemtrace.txt index a956d9b7f94..a956d9b7f94 100644 --- a/Documentation/vm/kmemtrace.txt +++ b/Documentation/trace/kmemtrace.txt diff --git a/Documentation/tracers/mmiotrace.txt b/Documentation/trace/mmiotrace.txt index 5731c67abc5..5731c67abc5 100644 --- a/Documentation/tracers/mmiotrace.txt +++ b/Documentation/trace/mmiotrace.txt diff --git a/Documentation/tracepoints.txt b/Documentation/trace/tracepoints.txt index c0e1ceed75a..c0e1ceed75a 100644 --- a/Documentation/tracepoints.txt +++ b/Documentation/trace/tracepoints.txt diff --git a/Documentation/vm/00-INDEX b/Documentation/vm/00-INDEX index 2131b00b63f..2f77ced35df 100644 --- a/Documentation/vm/00-INDEX +++ b/Documentation/vm/00-INDEX @@ -1,5 +1,7 @@ 00-INDEX - this file. +active_mm.txt + - An explanation from Linus about tsk->active_mm vs tsk->mm. balance - various information on memory balancing. hugetlbpage.txt diff --git a/Documentation/vm/active_mm.txt b/Documentation/vm/active_mm.txt new file mode 100644 index 00000000000..4ee1f643d89 --- /dev/null +++ b/Documentation/vm/active_mm.txt @@ -0,0 +1,83 @@ +List: linux-kernel +Subject: Re: active_mm +From: Linus Torvalds <torvalds () transmeta ! com> +Date: 1999-07-30 21:36:24 + +Cc'd to linux-kernel, because I don't write explanations all that often, +and when I do I feel better about more people reading them. + +On Fri, 30 Jul 1999, David Mosberger wrote: +> +> Is there a brief description someplace on how "mm" vs. "active_mm" in +> the task_struct are supposed to be used? (My apologies if this was +> discussed on the mailing lists---I just returned from vacation and +> wasn't able to follow linux-kernel for a while). + +Basically, the new setup is: + + - we have "real address spaces" and "anonymous address spaces". The + difference is that an anonymous address space doesn't care about the + user-level page tables at all, so when we do a context switch into an + anonymous address space we just leave the previous address space + active. + + The obvious use for a "anonymous address space" is any thread that + doesn't need any user mappings - all kernel threads basically fall into + this category, but even "real" threads can temporarily say that for + some amount of time they are not going to be interested in user space, + and that the scheduler might as well try to avoid wasting time on + switching the VM state around. Currently only the old-style bdflush + sync does that. + + - "tsk->mm" points to the "real address space". For an anonymous process, + tsk->mm will be NULL, for the logical reason that an anonymous process + really doesn't _have_ a real address space at all. + + - however, we obviously need to keep track of which address space we + "stole" for such an anonymous user. For that, we have "tsk->active_mm", + which shows what the currently active address space is. + + The rule is that for a process with a real address space (ie tsk->mm is + non-NULL) the active_mm obviously always has to be the same as the real + one. + + For a anonymous process, tsk->mm == NULL, and tsk->active_mm is the + "borrowed" mm while the anonymous process is running. When the + anonymous process gets scheduled away, the borrowed address space is + returned and cleared. + +To support all that, the "struct mm_struct" now has two counters: a +"mm_users" counter that is how many "real address space users" there are, +and a "mm_count" counter that is the number of "lazy" users (ie anonymous +users) plus one if there are any real users. + +Usually there is at least one real user, but it could be that the real +user exited on another CPU while a lazy user was still active, so you do +actually get cases where you have a address space that is _only_ used by +lazy users. That is often a short-lived state, because once that thread +gets scheduled away in favour of a real thread, the "zombie" mm gets +released because "mm_users" becomes zero. + +Also, a new rule is that _nobody_ ever has "init_mm" as a real MM any +more. "init_mm" should be considered just a "lazy context when no other +context is available", and in fact it is mainly used just at bootup when +no real VM has yet been created. So code that used to check + + if (current->mm == &init_mm) + +should generally just do + + if (!current->mm) + +instead (which makes more sense anyway - the test is basically one of "do +we have a user context", and is generally done by the page fault handler +and things like that). + +Anyway, I put a pre-patch-2.3.13-1 on ftp.kernel.org just a moment ago, +because it slightly changes the interfaces to accomodate the alpha (who +would have thought it, but the alpha actually ends up having one of the +ugliest context switch codes - unlike the other architectures where the MM +and register state is separate, the alpha PALcode joins the two, and you +need to switch both together). + +(From http://marc.info/?l=linux-kernel&m=93337278602211&w=2) diff --git a/Documentation/vm/unevictable-lru.txt b/Documentation/vm/unevictable-lru.txt index 0706a7282a8..2d70d0d9510 100644 --- a/Documentation/vm/unevictable-lru.txt +++ b/Documentation/vm/unevictable-lru.txt @@ -1,588 +1,691 @@ - -This document describes the Linux memory management "Unevictable LRU" -infrastructure and the use of this infrastructure to manage several types -of "unevictable" pages. The document attempts to provide the overall -rationale behind this mechanism and the rationale for some of the design -decisions that drove the implementation. The latter design rationale is -discussed in the context of an implementation description. Admittedly, one -can obtain the implementation details--the "what does it do?"--by reading the -code. One hopes that the descriptions below add value by provide the answer -to "why does it do that?". - -Unevictable LRU Infrastructure: - -The Unevictable LRU adds an additional LRU list to track unevictable pages -and to hide these pages from vmscan. This mechanism is based on a patch by -Larry Woodman of Red Hat to address several scalability problems with page + ============================== + UNEVICTABLE LRU INFRASTRUCTURE + ============================== + +======== +CONTENTS +======== + + (*) The Unevictable LRU + + - The unevictable page list. + - Memory control group interaction. + - Marking address spaces unevictable. + - Detecting Unevictable Pages. + - vmscan's handling of unevictable pages. + + (*) mlock()'d pages. + + - History. + - Basic management. + - mlock()/mlockall() system call handling. + - Filtering special vmas. + - munlock()/munlockall() system call handling. + - Migrating mlocked pages. + - mmap(MAP_LOCKED) system call handling. + - munmap()/exit()/exec() system call handling. + - try_to_unmap(). + - try_to_munlock() reverse map scan. + - Page reclaim in shrink_*_list(). + + +============ +INTRODUCTION +============ + +This document describes the Linux memory manager's "Unevictable LRU" +infrastructure and the use of this to manage several types of "unevictable" +pages. + +The document attempts to provide the overall rationale behind this mechanism +and the rationale for some of the design decisions that drove the +implementation. The latter design rationale is discussed in the context of an +implementation description. Admittedly, one can obtain the implementation +details - the "what does it do?" - by reading the code. One hopes that the +descriptions below add value by provide the answer to "why does it do that?". + + +=================== +THE UNEVICTABLE LRU +=================== + +The Unevictable LRU facility adds an additional LRU list to track unevictable +pages and to hide these pages from vmscan. This mechanism is based on a patch +by Larry Woodman of Red Hat to address several scalability problems with page reclaim in Linux. The problems have been observed at customer sites on large -memory x86_64 systems. For example, a non-numal x86_64 platform with 128GB -of main memory will have over 32 million 4k pages in a single zone. When a -large fraction of these pages are not evictable for any reason [see below], -vmscan will spend a lot of time scanning the LRU lists looking for the small -fraction of pages that are evictable. This can result in a situation where -all cpus are spending 100% of their time in vmscan for hours or days on end, -with the system completely unresponsive. - -The Unevictable LRU infrastructure addresses the following classes of -unevictable pages: - -+ page owned by ramfs -+ page mapped into SHM_LOCKed shared memory regions -+ page mapped into VM_LOCKED [mlock()ed] vmas - -The infrastructure might be able to handle other conditions that make pages +memory x86_64 systems. + +To illustrate this with an example, a non-NUMA x86_64 platform with 128GB of +main memory will have over 32 million 4k pages in a single zone. When a large +fraction of these pages are not evictable for any reason [see below], vmscan +will spend a lot of time scanning the LRU lists looking for the small fraction +of pages that are evictable. This can result in a situation where all CPUs are +spending 100% of their time in vmscan for hours or days on end, with the system +completely unresponsive. + +The unevictable list addresses the following classes of unevictable pages: + + (*) Those owned by ramfs. + + (*) Those mapped into SHM_LOCK'd shared memory regions. + + (*) Those mapped into VM_LOCKED [mlock()ed] VMAs. + +The infrastructure may also be able to handle other conditions that make pages unevictable, either by definition or by circumstance, in the future. -The Unevictable LRU List +THE UNEVICTABLE PAGE LIST +------------------------- The Unevictable LRU infrastructure consists of an additional, per-zone, LRU list called the "unevictable" list and an associated page flag, PG_unevictable, to -indicate that the page is being managed on the unevictable list. The -PG_unevictable flag is analogous to, and mutually exclusive with, the PG_active -flag in that it indicates on which LRU list a page resides when PG_lru is set. -The unevictable LRU list is source configurable based on the UNEVICTABLE_LRU -Kconfig option. +indicate that the page is being managed on the unevictable list. + +The PG_unevictable flag is analogous to, and mutually exclusive with, the +PG_active flag in that it indicates on which LRU list a page resides when +PG_lru is set. The unevictable list is compile-time configurable based on the +UNEVICTABLE_LRU Kconfig option. The Unevictable LRU infrastructure maintains unevictable pages on an additional LRU list for a few reasons: -1) We get to "treat unevictable pages just like we treat other pages in the - system, which means we get to use the same code to manipulate them, the - same code to isolate them (for migrate, etc.), the same code to keep track - of the statistics, etc..." [Rik van Riel] + (1) We get to "treat unevictable pages just like we treat other pages in the + system - which means we get to use the same code to manipulate them, the + same code to isolate them (for migrate, etc.), the same code to keep track + of the statistics, etc..." [Rik van Riel] + + (2) We want to be able to migrate unevictable pages between nodes for memory + defragmentation, workload management and memory hotplug. The linux kernel + can only migrate pages that it can successfully isolate from the LRU + lists. If we were to maintain pages elsewhere than on an LRU-like list, + where they can be found by isolate_lru_page(), we would prevent their + migration, unless we reworked migration code to find the unevictable pages + itself. -2) We want to be able to migrate unevictable pages between nodes--for memory - defragmentation, workload management and memory hotplug. The linux kernel - can only migrate pages that it can successfully isolate from the lru lists. - If we were to maintain pages elsewise than on an lru-like list, where they - can be found by isolate_lru_page(), we would prevent their migration, unless - we reworked migration code to find the unevictable pages. +The unevictable list does not differentiate between file-backed and anonymous, +swap-backed pages. This differentiation is only important while the pages are, +in fact, evictable. -The unevictable LRU list does not differentiate between file backed and swap -backed [anon] pages. This differentiation is only important while the pages -are, in fact, evictable. +The unevictable list benefits from the "arrayification" of the per-zone LRU +lists and statistics originally proposed and posted by Christoph Lameter. -The unevictable LRU list benefits from the "arrayification" of the per-zone -LRU lists and statistics originally proposed and posted by Christoph Lameter. +The unevictable list does not use the LRU pagevec mechanism. Rather, +unevictable pages are placed directly on the page's zone's unevictable list +under the zone lru_lock. This allows us to prevent the stranding of pages on +the unevictable list when one task has the page isolated from the LRU and other +tasks are changing the "evictability" state of the page. -The unevictable list does not use the lru pagevec mechanism. Rather, -unevictable pages are placed directly on the page's zone's unevictable -list under the zone lru_lock. The reason for this is to prevent stranding -of pages on the unevictable list when one task has the page isolated from the -lru and other tasks are changing the "evictability" state of the page. +MEMORY CONTROL GROUP INTERACTION +-------------------------------- -Unevictable LRU and Memory Controller Interaction +The unevictable LRU facility interacts with the memory control group [aka +memory controller; see Documentation/cgroups/memory.txt] by extending the +lru_list enum. + +The memory controller data structure automatically gets a per-zone unevictable +list as a result of the "arrayification" of the per-zone LRU lists (one per +lru_list enum element). The memory controller tracks the movement of pages to +and from the unevictable list. -The memory controller data structure automatically gets a per zone unevictable -lru list as a result of the "arrayification" of the per-zone LRU lists. The -memory controller tracks the movement of pages to and from the unevictable list. When a memory control group comes under memory pressure, the controller will not attempt to reclaim pages on the unevictable list. This has a couple of -effects. Because the pages are "hidden" from reclaim on the unevictable list, -the reclaim process can be more efficient, dealing only with pages that have -a chance of being reclaimed. On the other hand, if too many of the pages -charged to the control group are unevictable, the evictable portion of the -working set of the tasks in the control group may not fit into the available -memory. This can cause the control group to thrash or to oom-kill tasks. - - -Unevictable LRU: Detecting Unevictable Pages - -The function page_evictable(page, vma) in vmscan.c determines whether a -page is evictable or not. For ramfs pages and pages in SHM_LOCKed regions, -page_evictable() tests a new address space flag, AS_UNEVICTABLE, in the page's -address space using a wrapper function. Wrapper functions are used to set, -clear and test the flag to reduce the requirement for #ifdef's throughout the -source code. AS_UNEVICTABLE is set on ramfs inode/mapping when it is created. -This flag remains for the life of the inode. - -For shared memory regions, AS_UNEVICTABLE is set when an application -successfully SHM_LOCKs the region and is removed when the region is -SHM_UNLOCKed. Note that shmctl(SHM_LOCK, ...) does not populate the page -tables for the region as does, for example, mlock(). So, we make no special -effort to push any pages in the SHM_LOCKed region to the unevictable list. -Vmscan will do this when/if it encounters the pages during reclaim. On -SHM_UNLOCK, shmctl() scans the pages in the region and "rescues" them from the -unevictable list if no other condition keeps them unevictable. If a SHM_LOCKed -region is destroyed, the pages are also "rescued" from the unevictable list in -the process of freeing them. - -page_evictable() detects mlock()ed pages by testing an additional page flag, -PG_mlocked via the PageMlocked() wrapper. If the page is NOT mlocked, and a -non-NULL vma is supplied, page_evictable() will check whether the vma is +effects: + + (1) Because the pages are "hidden" from reclaim on the unevictable list, the + reclaim process can be more efficient, dealing only with pages that have a + chance of being reclaimed. + + (2) On the other hand, if too many of the pages charged to the control group + are unevictable, the evictable portion of the working set of the tasks in + the control group may not fit into the available memory. This can cause + the control group to thrash or to OOM-kill tasks. + + +MARKING ADDRESS SPACES UNEVICTABLE +---------------------------------- + +For facilities such as ramfs none of the pages attached to the address space +may be evicted. To prevent eviction of any such pages, the AS_UNEVICTABLE +address space flag is provided, and this can be manipulated by a filesystem +using a number of wrapper functions: + + (*) void mapping_set_unevictable(struct address_space *mapping); + + Mark the address space as being completely unevictable. + + (*) void mapping_clear_unevictable(struct address_space *mapping); + + Mark the address space as being evictable. + + (*) int mapping_unevictable(struct address_space *mapping); + + Query the address space, and return true if it is completely + unevictable. + +These are currently used in two places in the kernel: + + (1) By ramfs to mark the address spaces of its inodes when they are created, + and this mark remains for the life of the inode. + + (2) By SYSV SHM to mark SHM_LOCK'd address spaces until SHM_UNLOCK is called. + + Note that SHM_LOCK is not required to page in the locked pages if they're + swapped out; the application must touch the pages manually if it wants to + ensure they're in memory. + + +DETECTING UNEVICTABLE PAGES +--------------------------- + +The function page_evictable() in vmscan.c determines whether a page is +evictable or not using the query function outlined above [see section "Marking +address spaces unevictable"] to check the AS_UNEVICTABLE flag. + +For address spaces that are so marked after being populated (as SHM regions +might be), the lock action (eg: SHM_LOCK) can be lazy, and need not populate +the page tables for the region as does, for example, mlock(), nor need it make +any special effort to push any pages in the SHM_LOCK'd area to the unevictable +list. Instead, vmscan will do this if and when it encounters the pages during +a reclamation scan. + +On an unlock action (such as SHM_UNLOCK), the unlocker (eg: shmctl()) must scan +the pages in the region and "rescue" them from the unevictable list if no other +condition is keeping them unevictable. If an unevictable region is destroyed, +the pages are also "rescued" from the unevictable list in the process of +freeing them. + +page_evictable() also checks for mlocked pages by testing an additional page +flag, PG_mlocked (as wrapped by PageMlocked()). If the page is NOT mlocked, +and a non-NULL VMA is supplied, page_evictable() will check whether the VMA is VM_LOCKED via is_mlocked_vma(). is_mlocked_vma() will SetPageMlocked() and update the appropriate statistics if the vma is VM_LOCKED. This method allows efficient "culling" of pages in the fault path that are being faulted in to -VM_LOCKED vmas. +VM_LOCKED VMAs. -Unevictable Pages and Vmscan [shrink_*_list()] +VMSCAN'S HANDLING OF UNEVICTABLE PAGES +-------------------------------------- If unevictable pages are culled in the fault path, or moved to the unevictable -list at mlock() or mmap() time, vmscan will never encounter the pages until -they have become evictable again, for example, via munlock() and have been -"rescued" from the unevictable list. However, there may be situations where we -decide, for the sake of expediency, to leave a unevictable page on one of the -regular active/inactive LRU lists for vmscan to deal with. Vmscan checks for -such pages in all of the shrink_{active|inactive|page}_list() functions and -will "cull" such pages that it encounters--that is, it diverts those pages to -the unevictable list for the zone being scanned. - -There may be situations where a page is mapped into a VM_LOCKED vma, but the -page is not marked as PageMlocked. Such pages will make it all the way to +list at mlock() or mmap() time, vmscan will not encounter the pages until they +have become evictable again (via munlock() for example) and have been "rescued" +from the unevictable list. However, there may be situations where we decide, +for the sake of expediency, to leave a unevictable page on one of the regular +active/inactive LRU lists for vmscan to deal with. vmscan checks for such +pages in all of the shrink_{active|inactive|page}_list() functions and will +"cull" such pages that it encounters: that is, it diverts those pages to the +unevictable list for the zone being scanned. + +There may be situations where a page is mapped into a VM_LOCKED VMA, but the +page is not marked as PG_mlocked. Such pages will make it all the way to shrink_page_list() where they will be detected when vmscan walks the reverse -map in try_to_unmap(). If try_to_unmap() returns SWAP_MLOCK, shrink_page_list() -will cull the page at that point. +map in try_to_unmap(). If try_to_unmap() returns SWAP_MLOCK, +shrink_page_list() will cull the page at that point. -To "cull" an unevictable page, vmscan simply puts the page back on the lru -list using putback_lru_page()--the inverse operation to isolate_lru_page()-- -after dropping the page lock. Because the condition which makes the page -unevictable may change once the page is unlocked, putback_lru_page() will -recheck the unevictable state of a page that it places on the unevictable lru -list. If the page has become unevictable, putback_lru_page() removes it from -the list and retries, including the page_unevictable() test. Because such a -race is a rare event and movement of pages onto the unevictable list should be -rare, these extra evictabilty checks should not occur in the majority of calls -to putback_lru_page(). +To "cull" an unevictable page, vmscan simply puts the page back on the LRU list +using putback_lru_page() - the inverse operation to isolate_lru_page() - after +dropping the page lock. Because the condition which makes the page unevictable +may change once the page is unlocked, putback_lru_page() will recheck the +unevictable state of a page that it places on the unevictable list. If the +page has become unevictable, putback_lru_page() removes it from the list and +retries, including the page_unevictable() test. Because such a race is a rare +event and movement of pages onto the unevictable list should be rare, these +extra evictabilty checks should not occur in the majority of calls to +putback_lru_page(). -Mlocked Page: Prior Work +============= +MLOCKED PAGES +============= -The "Unevictable Mlocked Pages" infrastructure is based on work originally +The unevictable page list is also useful for mlock(), in addition to ramfs and +SYSV SHM. Note that mlock() is only available in CONFIG_MMU=y situations; in +NOMMU situations, all mappings are effectively mlocked. + + +HISTORY +------- + +The "Unevictable mlocked Pages" infrastructure is based on work originally posted by Nick Piggin in an RFC patch entitled "mm: mlocked pages off LRU". -Nick posted his patch as an alternative to a patch posted by Christoph -Lameter to achieve the same objective--hiding mlocked pages from vmscan. -In Nick's patch, he used one of the struct page lru list link fields as a count -of VM_LOCKED vmas that map the page. This use of the link field for a count -prevented the management of the pages on an LRU list. Thus, mlocked pages were -not migratable as isolate_lru_page() could not find them and the lru list link -field was not available to the migration subsystem. Nick resolved this by -putting mlocked pages back on the lru list before attempting to isolate them, -thus abandoning the count of VM_LOCKED vmas. When Nick's patch was integrated -with the Unevictable LRU work, the count was replaced by walking the reverse -map to determine whether any VM_LOCKED vmas mapped the page. More on this -below. - - -Mlocked Pages: Basic Management - -Mlocked pages--pages mapped into a VM_LOCKED vma--represent one class of -unevictable pages. When such a page has been "noticed" by the memory -management subsystem, the page is marked with the PG_mlocked [PageMlocked()] -flag. A PageMlocked() page will be placed on the unevictable LRU list when -it is added to the LRU. Pages can be "noticed" by memory management in -several places: - -1) in the mlock()/mlockall() system call handlers. -2) in the mmap() system call handler when mmap()ing a region with the - MAP_LOCKED flag, or mmap()ing a region in a task that has called - mlockall() with the MCL_FUTURE flag. Both of these conditions result - in the VM_LOCKED flag being set for the vma. -3) in the fault path, if mlocked pages are "culled" in the fault path, - and when a VM_LOCKED stack segment is expanded. -4) as mentioned above, in vmscan:shrink_page_list() when attempting to - reclaim a page in a VM_LOCKED vma via try_to_unmap(). - -Mlocked pages become unlocked and rescued from the unevictable list when: - -1) mapped in a range unlocked via the munlock()/munlockall() system calls. -2) munmapped() out of the last VM_LOCKED vma that maps the page, including - unmapping at task exit. -3) when the page is truncated from the last VM_LOCKED vma of an mmap()ed file. -4) before a page is COWed in a VM_LOCKED vma. - - -Mlocked Pages: mlock()/mlockall() System Call Handling +Nick posted his patch as an alternative to a patch posted by Christoph Lameter +to achieve the same objective: hiding mlocked pages from vmscan. + +In Nick's patch, he used one of the struct page LRU list link fields as a count +of VM_LOCKED VMAs that map the page. This use of the link field for a count +prevented the management of the pages on an LRU list, and thus mlocked pages +were not migratable as isolate_lru_page() could not find them, and the LRU list +link field was not available to the migration subsystem. + +Nick resolved this by putting mlocked pages back on the lru list before +attempting to isolate them, thus abandoning the count of VM_LOCKED VMAs. When +Nick's patch was integrated with the Unevictable LRU work, the count was +replaced by walking the reverse map to determine whether any VM_LOCKED VMAs +mapped the page. More on this below. + + +BASIC MANAGEMENT +---------------- + +mlocked pages - pages mapped into a VM_LOCKED VMA - are a class of unevictable +pages. When such a page has been "noticed" by the memory management subsystem, +the page is marked with the PG_mlocked flag. This can be manipulated using the +PageMlocked() functions. + +A PG_mlocked page will be placed on the unevictable list when it is added to +the LRU. Such pages can be "noticed" by memory management in several places: + + (1) in the mlock()/mlockall() system call handlers; + + (2) in the mmap() system call handler when mmapping a region with the + MAP_LOCKED flag; + + (3) mmapping a region in a task that has called mlockall() with the MCL_FUTURE + flag + + (4) in the fault path, if mlocked pages are "culled" in the fault path, + and when a VM_LOCKED stack segment is expanded; or + + (5) as mentioned above, in vmscan:shrink_page_list() when attempting to + reclaim a page in a VM_LOCKED VMA via try_to_unmap() + +all of which result in the VM_LOCKED flag being set for the VMA if it doesn't +already have it set. + +mlocked pages become unlocked and rescued from the unevictable list when: + + (1) mapped in a range unlocked via the munlock()/munlockall() system calls; + + (2) munmap()'d out of the last VM_LOCKED VMA that maps the page, including + unmapping at task exit; + + (3) when the page is truncated from the last VM_LOCKED VMA of an mmapped file; + or + + (4) before a page is COW'd in a VM_LOCKED VMA. + + +mlock()/mlockall() SYSTEM CALL HANDLING +--------------------------------------- Both [do_]mlock() and [do_]mlockall() system call handlers call mlock_fixup() -for each vma in the range specified by the call. In the case of mlockall(), +for each VMA in the range specified by the call. In the case of mlockall(), this is the entire active address space of the task. Note that mlock_fixup() -is used for both mlock()ing and munlock()ing a range of memory. A call to -mlock() an already VM_LOCKED vma, or to munlock() a vma that is not VM_LOCKED -is treated as a no-op--mlock_fixup() simply returns. - -If the vma passes some filtering described in "Mlocked Pages: Filtering Vmas" -below, mlock_fixup() will attempt to merge the vma with its neighbors or split -off a subset of the vma if the range does not cover the entire vma. Once the -vma has been merged or split or neither, mlock_fixup() will call -__mlock_vma_pages_range() to fault in the pages via get_user_pages() and -to mark the pages as mlocked via mlock_vma_page(). - -Note that the vma being mlocked might be mapped with PROT_NONE. In this case, -get_user_pages() will be unable to fault in the pages. That's OK. If pages -do end up getting faulted into this VM_LOCKED vma, we'll handle them in the +is used for both mlocking and munlocking a range of memory. A call to mlock() +an already VM_LOCKED VMA, or to munlock() a VMA that is not VM_LOCKED is +treated as a no-op, and mlock_fixup() simply returns. + +If the VMA passes some filtering as described in "Filtering Special Vmas" +below, mlock_fixup() will attempt to merge the VMA with its neighbors or split +off a subset of the VMA if the range does not cover the entire VMA. Once the +VMA has been merged or split or neither, mlock_fixup() will call +__mlock_vma_pages_range() to fault in the pages via get_user_pages() and to +mark the pages as mlocked via mlock_vma_page(). + +Note that the VMA being mlocked might be mapped with PROT_NONE. In this case, +get_user_pages() will be unable to fault in the pages. That's okay. If pages +do end up getting faulted into this VM_LOCKED VMA, we'll handle them in the fault path or in vmscan. Also note that a page returned by get_user_pages() could be truncated or -migrated out from under us, while we're trying to mlock it. To detect -this, __mlock_vma_pages_range() tests the page_mapping after acquiring -the page lock. If the page is still associated with its mapping, we'll -go ahead and call mlock_vma_page(). If the mapping is gone, we just -unlock the page and move on. Worse case, this results in page mapped -in a VM_LOCKED vma remaining on a normal LRU list without being -PageMlocked(). Again, vmscan will detect and cull such pages. - -mlock_vma_page(), called with the page locked [N.B., not "mlocked"], will -TestSetPageMlocked() for each page returned by get_user_pages(). We use -TestSetPageMlocked() because the page might already be mlocked by another -task/vma and we don't want to do extra work. We especially do not want to -count an mlocked page more than once in the statistics. If the page was -already mlocked, mlock_vma_page() is done. +migrated out from under us, while we're trying to mlock it. To detect this, +__mlock_vma_pages_range() checks page_mapping() after acquiring the page lock. +If the page is still associated with its mapping, we'll go ahead and call +mlock_vma_page(). If the mapping is gone, we just unlock the page and move on. +In the worst case, this will result in a page mapped in a VM_LOCKED VMA +remaining on a normal LRU list without being PageMlocked(). Again, vmscan will +detect and cull such pages. + +mlock_vma_page() will call TestSetPageMlocked() for each page returned by +get_user_pages(). We use TestSetPageMlocked() because the page might already +be mlocked by another task/VMA and we don't want to do extra work. We +especially do not want to count an mlocked page more than once in the +statistics. If the page was already mlocked, mlock_vma_page() need do nothing +more. If the page was NOT already mlocked, mlock_vma_page() attempts to isolate the page from the LRU, as it is likely on the appropriate active or inactive list -at that time. If the isolate_lru_page() succeeds, mlock_vma_page() will -putback the page--putback_lru_page()--which will notice that the page is now -mlocked and divert the page to the zone's unevictable LRU list. If +at that time. If the isolate_lru_page() succeeds, mlock_vma_page() will put +back the page - by calling putback_lru_page() - which will notice that the page +is now mlocked and divert the page to the zone's unevictable list. If mlock_vma_page() is unable to isolate the page from the LRU, vmscan will handle -it later if/when it attempts to reclaim the page. +it later if and when it attempts to reclaim the page. -Mlocked Pages: Filtering Special Vmas +FILTERING SPECIAL VMAS +---------------------- -mlock_fixup() filters several classes of "special" vmas: +mlock_fixup() filters several classes of "special" VMAs: -1) vmas with VM_IO|VM_PFNMAP set are skipped entirely. The pages behind +1) VMAs with VM_IO or VM_PFNMAP set are skipped entirely. The pages behind these mappings are inherently pinned, so we don't need to mark them as - mlocked. In any case, most of the pages have no struct page in which to - so mark the page. Because of this, get_user_pages() will fail for these - vmas, so there is no sense in attempting to visit them. - -2) vmas mapping hugetlbfs page are already effectively pinned into memory. - We don't need nor want to mlock() these pages. However, to preserve the - prior behavior of mlock()--before the unevictable/mlock changes-- - mlock_fixup() will call make_pages_present() in the hugetlbfs vma range - to allocate the huge pages and populate the ptes. - -3) vmas with VM_DONTEXPAND|VM_RESERVED are generally user space mappings of - kernel pages, such as the vdso page, relay channel pages, etc. These pages + mlocked. In any case, most of the pages have no struct page in which to so + mark the page. Because of this, get_user_pages() will fail for these VMAs, + so there is no sense in attempting to visit them. + +2) VMAs mapping hugetlbfs page are already effectively pinned into memory. We + neither need nor want to mlock() these pages. However, to preserve the + prior behavior of mlock() - before the unevictable/mlock changes - + mlock_fixup() will call make_pages_present() in the hugetlbfs VMA range to + allocate the huge pages and populate the ptes. + +3) VMAs with VM_DONTEXPAND or VM_RESERVED are generally userspace mappings of + kernel pages, such as the VDSO page, relay channel pages, etc. These pages are inherently unevictable and are not managed on the LRU lists. - mlock_fixup() treats these vmas the same as hugetlbfs vmas. It calls + mlock_fixup() treats these VMAs the same as hugetlbfs VMAs. It calls make_pages_present() to populate the ptes. -Note that for all of these special vmas, mlock_fixup() does not set the +Note that for all of these special VMAs, mlock_fixup() does not set the VM_LOCKED flag. Therefore, we won't have to deal with them later during -munlock() or munmap()--for example, at task exit. Neither does mlock_fixup() -account these vmas against the task's "locked_vm". - -Mlocked Pages: Downgrading the Mmap Semaphore. - -mlock_fixup() must be called with the mmap semaphore held for write, because -it may have to merge or split vmas. However, mlocking a large region of -memory can take a long time--especially if vmscan must reclaim pages to -satisfy the regions requirements. Faulting in a large region with the mmap -semaphore held for write can hold off other faults on the address space, in -the case of a multi-threaded task. It can also hold off scans of the task's -address space via /proc. While testing under heavy load, it was observed that -the ps(1) command could be held off for many minutes while a large segment was -mlock()ed down. - -To address this issue, and to make the system more responsive during mlock()ing -of large segments, mlock_fixup() downgrades the mmap semaphore to read mode -during the call to __mlock_vma_pages_range(). This works fine. However, the -callers of mlock_fixup() expect the semaphore to be returned in write mode. -So, mlock_fixup() "upgrades" the semphore to write mode. Linux does not -support an atomic upgrade_sem() call, so mlock_fixup() must drop the semaphore -and reacquire it in write mode. In a multi-threaded task, it is possible for -the task memory map to change while the semaphore is dropped. Therefore, -mlock_fixup() looks up the vma at the range start address after reacquiring -the semaphore in write mode and verifies that it still covers the original -range. If not, mlock_fixup() returns an error [-EAGAIN]. All callers of -mlock_fixup() have been changed to deal with this new error condition. - -Note: when munlocking a region, all of the pages should already be resident-- -unless we have racing threads mlocking() and munlocking() regions. So, -unlocking should not have to wait for page allocations nor faults of any kind. -Therefore mlock_fixup() does not downgrade the semaphore for munlock(). - - -Mlocked Pages: munlock()/munlockall() System Call Handling - -The munlock() and munlockall() system calls are handled by the same functions-- -do_mlock[all]()--as the mlock() and mlockall() system calls with the unlock -vs lock operation indicated by an argument. So, these system calls are also -handled by mlock_fixup(). Again, if called for an already munlock()ed vma, -mlock_fixup() simply returns. Because of the vma filtering discussed above, -VM_LOCKED will not be set in any "special" vmas. So, these vmas will be +munlock(), munmap() or task exit. Neither does mlock_fixup() account these +VMAs against the task's "locked_vm". + + +munlock()/munlockall() SYSTEM CALL HANDLING +------------------------------------------- + +The munlock() and munlockall() system calls are handled by the same functions - +do_mlock[all]() - as the mlock() and mlockall() system calls with the unlock vs +lock operation indicated by an argument. So, these system calls are also +handled by mlock_fixup(). Again, if called for an already munlocked VMA, +mlock_fixup() simply returns. Because of the VMA filtering discussed above, +VM_LOCKED will not be set in any "special" VMAs. So, these VMAs will be ignored for munlock. -If the vma is VM_LOCKED, mlock_fixup() again attempts to merge or split off -the specified range. The range is then munlocked via the function -__mlock_vma_pages_range()--the same function used to mlock a vma range-- +If the VMA is VM_LOCKED, mlock_fixup() again attempts to merge or split off the +specified range. The range is then munlocked via the function +__mlock_vma_pages_range() - the same function used to mlock a VMA range - passing a flag to indicate that munlock() is being performed. -Because the vma access protections could have been changed to PROT_NONE after +Because the VMA access protections could have been changed to PROT_NONE after faulting in and mlocking pages, get_user_pages() was unreliable for visiting -these pages for munlocking. Because we don't want to leave pages mlocked(), +these pages for munlocking. Because we don't want to leave pages mlocked, get_user_pages() was enhanced to accept a flag to ignore the permissions when -fetching the pages--all of which should be resident as a result of previous -mlock()ing. +fetching the pages - all of which should be resident as a result of previous +mlocking. For munlock(), __mlock_vma_pages_range() unlocks individual pages by calling munlock_vma_page(). munlock_vma_page() unconditionally clears the PG_mlocked -flag using TestClearPageMlocked(). As with mlock_vma_page(), munlock_vma_page() -use the Test*PageMlocked() function to handle the case where the page might -have already been unlocked by another task. If the page was mlocked, -munlock_vma_page() updates that zone statistics for the number of mlocked -pages. Note, however, that at this point we haven't checked whether the page -is mapped by other VM_LOCKED vmas. - -We can't call try_to_munlock(), the function that walks the reverse map to check -for other VM_LOCKED vmas, without first isolating the page from the LRU. +flag using TestClearPageMlocked(). As with mlock_vma_page(), +munlock_vma_page() use the Test*PageMlocked() function to handle the case where +the page might have already been unlocked by another task. If the page was +mlocked, munlock_vma_page() updates that zone statistics for the number of +mlocked pages. Note, however, that at this point we haven't checked whether +the page is mapped by other VM_LOCKED VMAs. + +We can't call try_to_munlock(), the function that walks the reverse map to +check for other VM_LOCKED VMAs, without first isolating the page from the LRU. try_to_munlock() is a variant of try_to_unmap() and thus requires that the page -not be on an lru list. [More on these below.] However, the call to -isolate_lru_page() could fail, in which case we couldn't try_to_munlock(). -So, we go ahead and clear PG_mlocked up front, as this might be the only chance -we have. If we can successfully isolate the page, we go ahead and +not be on an LRU list [more on these below]. However, the call to +isolate_lru_page() could fail, in which case we couldn't try_to_munlock(). So, +we go ahead and clear PG_mlocked up front, as this might be the only chance we +have. If we can successfully isolate the page, we go ahead and try_to_munlock(), which will restore the PG_mlocked flag and update the zone -page statistics if it finds another vma holding the page mlocked. If we fail +page statistics if it finds another VMA holding the page mlocked. If we fail to isolate the page, we'll have left a potentially mlocked page on the LRU. -This is fine, because we'll catch it later when/if vmscan tries to reclaim the -page. This should be relatively rare. - -Mlocked Pages: Migrating Them... - -A page that is being migrated has been isolated from the lru lists and is -held locked across unmapping of the page, updating the page's mapping -[address_space] entry and copying the contents and state, until the -page table entry has been replaced with an entry that refers to the new -page. Linux supports migration of mlocked pages and other unevictable -pages. This involves simply moving the PageMlocked and PageUnevictable states -from the old page to the new page. - -Note that page migration can race with mlocking or munlocking of the same -page. This has been discussed from the mlock/munlock perspective in the -respective sections above. Both processes [migration, m[un]locking], hold -the page locked. This provides the first level of synchronization. Page -migration zeros out the page_mapping of the old page before unlocking it, -so m[un]lock can skip these pages by testing the page mapping under page -lock. - -When completing page migration, we place the new and old pages back onto the -lru after dropping the page lock. The "unneeded" page--old page on success, -new page on failure--will be freed when the reference count held by the -migration process is released. To ensure that we don't strand pages on the -unevictable list because of a race between munlock and migration, page -migration uses the putback_lru_page() function to add migrated pages back to -the lru. - - -Mlocked Pages: mmap(MAP_LOCKED) System Call Handling +This is fine, because we'll catch it later if and if vmscan tries to reclaim +the page. This should be relatively rare. + + +MIGRATING MLOCKED PAGES +----------------------- + +A page that is being migrated has been isolated from the LRU lists and is held +locked across unmapping of the page, updating the page's address space entry +and copying the contents and state, until the page table entry has been +replaced with an entry that refers to the new page. Linux supports migration +of mlocked pages and other unevictable pages. This involves simply moving the +PG_mlocked and PG_unevictable states from the old page to the new page. + +Note that page migration can race with mlocking or munlocking of the same page. +This has been discussed from the mlock/munlock perspective in the respective +sections above. Both processes (migration and m[un]locking) hold the page +locked. This provides the first level of synchronization. Page migration +zeros out the page_mapping of the old page before unlocking it, so m[un]lock +can skip these pages by testing the page mapping under page lock. + +To complete page migration, we place the new and old pages back onto the LRU +after dropping the page lock. The "unneeded" page - old page on success, new +page on failure - will be freed when the reference count held by the migration +process is released. To ensure that we don't strand pages on the unevictable +list because of a race between munlock and migration, page migration uses the +putback_lru_page() function to add migrated pages back to the LRU. + + +mmap(MAP_LOCKED) SYSTEM CALL HANDLING +------------------------------------- In addition the the mlock()/mlockall() system calls, an application can request -that a region of memory be mlocked using the MAP_LOCKED flag with the mmap() +that a region of memory be mlocked supplying the MAP_LOCKED flag to the mmap() call. Furthermore, any mmap() call or brk() call that expands the heap by a task that has previously called mlockall() with the MCL_FUTURE flag will result -in the newly mapped memory being mlocked. Before the unevictable/mlock changes, -the kernel simply called make_pages_present() to allocate pages and populate -the page table. +in the newly mapped memory being mlocked. Before the unevictable/mlock +changes, the kernel simply called make_pages_present() to allocate pages and +populate the page table. To mlock a range of memory under the unevictable/mlock infrastructure, the mmap() handler and task address space expansion functions call mlock_vma_pages_range() specifying the vma and the address range to mlock. -mlock_vma_pages_range() filters vmas like mlock_fixup(), as described above in -"Mlocked Pages: Filtering Vmas". It will clear the VM_LOCKED flag, which will -have already been set by the caller, in filtered vmas. Thus these vma's need -not be visited for munlock when the region is unmapped. +mlock_vma_pages_range() filters VMAs like mlock_fixup(), as described above in +"Filtering Special VMAs". It will clear the VM_LOCKED flag, which will have +already been set by the caller, in filtered VMAs. Thus these VMA's need not be +visited for munlock when the region is unmapped. -For "normal" vmas, mlock_vma_pages_range() calls __mlock_vma_pages_range() to +For "normal" VMAs, mlock_vma_pages_range() calls __mlock_vma_pages_range() to fault/allocate the pages and mlock them. Again, like mlock_fixup(), mlock_vma_pages_range() downgrades the mmap semaphore to read mode before -attempting to fault/allocate and mlock the pages; and "upgrades" the semaphore +attempting to fault/allocate and mlock the pages and "upgrades" the semaphore back to write mode before returning. -The callers of mlock_vma_pages_range() will have already added the memory -range to be mlocked to the task's "locked_vm". To account for filtered vmas, +The callers of mlock_vma_pages_range() will have already added the memory range +to be mlocked to the task's "locked_vm". To account for filtered VMAs, mlock_vma_pages_range() returns the number of pages NOT mlocked. All of the -callers then subtract a non-negative return value from the task's locked_vm. -A negative return value represent an error--for example, from get_user_pages() -attempting to fault in a vma with PROT_NONE access. In this case, we leave -the memory range accounted as locked_vm, as the protections could be changed -later and pages allocated into that region. +callers then subtract a non-negative return value from the task's locked_vm. A +negative return value represent an error - for example, from get_user_pages() +attempting to fault in a VMA with PROT_NONE access. In this case, we leave the +memory range accounted as locked_vm, as the protections could be changed later +and pages allocated into that region. -Mlocked Pages: munmap()/exit()/exec() System Call Handling +munmap()/exit()/exec() SYSTEM CALL HANDLING +------------------------------------------- When unmapping an mlocked region of memory, whether by an explicit call to munmap() or via an internal unmap from exit() or exec() processing, we must -munlock the pages if we're removing the last VM_LOCKED vma that maps the pages. +munlock the pages if we're removing the last VM_LOCKED VMA that maps the pages. Before the unevictable/mlock changes, mlocking did not mark the pages in any way, so unmapping them required no processing. To munlock a range of memory under the unevictable/mlock infrastructure, the -munmap() hander and task address space tear down function call +munmap() handler and task address space call tear down function munlock_vma_pages_all(). The name reflects the observation that one always -specifies the entire vma range when munlock()ing during unmap of a region. -Because of the vma filtering when mlocking() regions, only "normal" vmas that +specifies the entire VMA range when munlock()ing during unmap of a region. +Because of the VMA filtering when mlocking() regions, only "normal" VMAs that actually contain mlocked pages will be passed to munlock_vma_pages_all(). -munlock_vma_pages_all() clears the VM_LOCKED vma flag and, like mlock_fixup() +munlock_vma_pages_all() clears the VM_LOCKED VMA flag and, like mlock_fixup() for the munlock case, calls __munlock_vma_pages_range() to walk the page table -for the vma's memory range and munlock_vma_page() each resident page mapped by -the vma. This effectively munlocks the page, only if this is the last -VM_LOCKED vma that maps the page. - +for the VMA's memory range and munlock_vma_page() each resident page mapped by +the VMA. This effectively munlocks the page, only if this is the last +VM_LOCKED VMA that maps the page. -Mlocked Page: try_to_unmap() -[Note: the code changes represented by this section are really quite small -compared to the text to describe what happening and why, and to discuss the -implications.] +try_to_unmap() +-------------- -Pages can, of course, be mapped into multiple vmas. Some of these vmas may +Pages can, of course, be mapped into multiple VMAs. Some of these VMAs may have VM_LOCKED flag set. It is possible for a page mapped into one or more -VM_LOCKED vmas not to have the PG_mlocked flag set and therefore reside on one -of the active or inactive LRU lists. This could happen if, for example, a -task in the process of munlock()ing the page could not isolate the page from -the LRU. As a result, vmscan/shrink_page_list() might encounter such a page -as described in "Unevictable Pages and Vmscan [shrink_*_list()]". To -handle this situation, try_to_unmap() has been enhanced to check for VM_LOCKED -vmas while it is walking a page's reverse map. +VM_LOCKED VMAs not to have the PG_mlocked flag set and therefore reside on one +of the active or inactive LRU lists. This could happen if, for example, a task +in the process of munlocking the page could not isolate the page from the LRU. +As a result, vmscan/shrink_page_list() might encounter such a page as described +in section "vmscan's handling of unevictable pages". To handle this situation, +try_to_unmap() checks for VM_LOCKED VMAs while it is walking a page's reverse +map. try_to_unmap() is always called, by either vmscan for reclaim or for page -migration, with the argument page locked and isolated from the LRU. BUG_ON() -assertions enforce this requirement. Separate functions handle anonymous and -mapped file pages, as these types of pages have different reverse map -mechanisms. - - try_to_unmap_anon() - -To unmap anonymous pages, each vma in the list anchored in the anon_vma must be -visited--at least until a VM_LOCKED vma is encountered. If the page is being -unmapped for migration, VM_LOCKED vmas do not stop the process because mlocked -pages are migratable. However, for reclaim, if the page is mapped into a -VM_LOCKED vma, the scan stops. try_to_unmap() attempts to acquire the mmap -semphore of the mm_struct to which the vma belongs in read mode. If this is -successful, try_to_unmap() will mlock the page via mlock_vma_page()--we -wouldn't have gotten to try_to_unmap() if the page were already mlocked--and -will return SWAP_MLOCK, indicating that the page is unevictable. If the -mmap semaphore cannot be acquired, we are not sure whether the page is really -unevictable or not. In this case, try_to_unmap() will return SWAP_AGAIN. - - try_to_unmap_file() -- linear mappings - -Unmapping of a mapped file page works the same, except that the scan visits -all vmas that maps the page's index/page offset in the page's mapping's -reverse map priority search tree. It must also visit each vma in the page's -mapping's non-linear list, if the list is non-empty. As for anonymous pages, -on encountering a VM_LOCKED vma for a mapped file page, try_to_unmap() will -attempt to acquire the associated mm_struct's mmap semaphore to mlock the page, -returning SWAP_MLOCK if this is successful, and SWAP_AGAIN, if not. - - try_to_unmap_file() -- non-linear mappings - -If a page's mapping contains a non-empty non-linear mapping vma list, then -try_to_un{map|lock}() must also visit each vma in that list to determine -whether the page is mapped in a VM_LOCKED vma. Again, the scan must visit -all vmas in the non-linear list to ensure that the pages is not/should not be -mlocked. If a VM_LOCKED vma is found in the list, the scan could terminate. -However, there is no easy way to determine whether the page is actually mapped -in a given vma--either for unmapping or testing whether the VM_LOCKED vma -actually pins the page. - -So, try_to_unmap_file() handles non-linear mappings by scanning a certain -number of pages--a "cluster"--in each non-linear vma associated with the page's -mapping, for each file mapped page that vmscan tries to unmap. If this happens -to unmap the page we're trying to unmap, try_to_unmap() will notice this on -return--(page_mapcount(page) == 0)--and return SWAP_SUCCESS. Otherwise, it -will return SWAP_AGAIN, causing vmscan to recirculate this page. We take -advantage of the cluster scan in try_to_unmap_cluster() as follows: - -For each non-linear vma, try_to_unmap_cluster() attempts to acquire the mmap -semaphore of the associated mm_struct for read without blocking. If this -attempt is successful and the vma is VM_LOCKED, try_to_unmap_cluster() will -retain the mmap semaphore for the scan; otherwise it drops it here. Then, -for each page in the cluster, if we're holding the mmap semaphore for a locked -vma, try_to_unmap_cluster() calls mlock_vma_page() to mlock the page. This -call is a no-op if the page is already locked, but will mlock any pages in -the non-linear mapping that happen to be unlocked. If one of the pages so -mlocked is the page passed in to try_to_unmap(), try_to_unmap_cluster() will -return SWAP_MLOCK, rather than the default SWAP_AGAIN. This will allow vmscan -to cull the page, rather than recirculating it on the inactive list. Again, -if try_to_unmap_cluster() cannot acquire the vma's mmap sem, it returns -SWAP_AGAIN, indicating that the page is mapped by a VM_LOCKED vma, but -couldn't be mlocked. - - -Mlocked pages: try_to_munlock() Reverse Map Scan - -TODO/FIXME: a better name might be page_mlocked()--analogous to the -page_referenced() reverse map walker. - -When munlock_vma_page()--see "Mlocked Pages: munlock()/munlockall() -System Call Handling" above--tries to munlock a page, it needs to -determine whether or not the page is mapped by any VM_LOCKED vma, without -actually attempting to unmap all ptes from the page. For this purpose, the -unevictable/mlock infrastructure introduced a variant of try_to_unmap() called -try_to_munlock(). +migration, with the argument page locked and isolated from the LRU. Separate +functions handle anonymous and mapped file pages, as these types of pages have +different reverse map mechanisms. + + (*) try_to_unmap_anon() + + To unmap anonymous pages, each VMA in the list anchored in the anon_vma + must be visited - at least until a VM_LOCKED VMA is encountered. If the + page is being unmapped for migration, VM_LOCKED VMAs do not stop the + process because mlocked pages are migratable. However, for reclaim, if + the page is mapped into a VM_LOCKED VMA, the scan stops. + + try_to_unmap_anon() attempts to acquire in read mode the mmap semphore of + the mm_struct to which the VMA belongs. If this is successful, it will + mlock the page via mlock_vma_page() - we wouldn't have gotten to + try_to_unmap_anon() if the page were already mlocked - and will return + SWAP_MLOCK, indicating that the page is unevictable. + + If the mmap semaphore cannot be acquired, we are not sure whether the page + is really unevictable or not. In this case, try_to_unmap_anon() will + return SWAP_AGAIN. + + (*) try_to_unmap_file() - linear mappings + + Unmapping of a mapped file page works the same as for anonymous mappings, + except that the scan visits all VMAs that map the page's index/page offset + in the page's mapping's reverse map priority search tree. It also visits + each VMA in the page's mapping's non-linear list, if the list is + non-empty. + + As for anonymous pages, on encountering a VM_LOCKED VMA for a mapped file + page, try_to_unmap_file() will attempt to acquire the associated + mm_struct's mmap semaphore to mlock the page, returning SWAP_MLOCK if this + is successful, and SWAP_AGAIN, if not. + + (*) try_to_unmap_file() - non-linear mappings + + If a page's mapping contains a non-empty non-linear mapping VMA list, then + try_to_un{map|lock}() must also visit each VMA in that list to determine + whether the page is mapped in a VM_LOCKED VMA. Again, the scan must visit + all VMAs in the non-linear list to ensure that the pages is not/should not + be mlocked. + + If a VM_LOCKED VMA is found in the list, the scan could terminate. + However, there is no easy way to determine whether the page is actually + mapped in a given VMA - either for unmapping or testing whether the + VM_LOCKED VMA actually pins the page. + + try_to_unmap_file() handles non-linear mappings by scanning a certain + number of pages - a "cluster" - in each non-linear VMA associated with the + page's mapping, for each file mapped page that vmscan tries to unmap. If + this happens to unmap the page we're trying to unmap, try_to_unmap() will + notice this on return (page_mapcount(page) will be 0) and return + SWAP_SUCCESS. Otherwise, it will return SWAP_AGAIN, causing vmscan to + recirculate this page. We take advantage of the cluster scan in + try_to_unmap_cluster() as follows: + + For each non-linear VMA, try_to_unmap_cluster() attempts to acquire the + mmap semaphore of the associated mm_struct for read without blocking. + + If this attempt is successful and the VMA is VM_LOCKED, + try_to_unmap_cluster() will retain the mmap semaphore for the scan; + otherwise it drops it here. + + Then, for each page in the cluster, if we're holding the mmap semaphore + for a locked VMA, try_to_unmap_cluster() calls mlock_vma_page() to + mlock the page. This call is a no-op if the page is already locked, + but will mlock any pages in the non-linear mapping that happen to be + unlocked. + + If one of the pages so mlocked is the page passed in to try_to_unmap(), + try_to_unmap_cluster() will return SWAP_MLOCK, rather than the default + SWAP_AGAIN. This will allow vmscan to cull the page, rather than + recirculating it on the inactive list. + + Again, if try_to_unmap_cluster() cannot acquire the VMA's mmap sem, it + returns SWAP_AGAIN, indicating that the page is mapped by a VM_LOCKED + VMA, but couldn't be mlocked. + + +try_to_munlock() REVERSE MAP SCAN +--------------------------------- + + [!] TODO/FIXME: a better name might be page_mlocked() - analogous to the + page_referenced() reverse map walker. + +When munlock_vma_page() [see section "munlock()/munlockall() System Call +Handling" above] tries to munlock a page, it needs to determine whether or not +the page is mapped by any VM_LOCKED VMA without actually attempting to unmap +all PTEs from the page. For this purpose, the unevictable/mlock infrastructure +introduced a variant of try_to_unmap() called try_to_munlock(). try_to_munlock() calls the same functions as try_to_unmap() for anonymous and mapped file pages with an additional argument specifing unlock versus unmap processing. Again, these functions walk the respective reverse maps looking -for VM_LOCKED vmas. When such a vma is found for anonymous pages and file +for VM_LOCKED VMAs. When such a VMA is found for anonymous pages and file pages mapped in linear VMAs, as in the try_to_unmap() case, the functions attempt to acquire the associated mmap semphore, mlock the page via mlock_vma_page() and return SWAP_MLOCK. This effectively undoes the pre-clearing of the page's PG_mlocked done by munlock_vma_page. -If try_to_unmap() is unable to acquire a VM_LOCKED vma's associated mmap -semaphore, it will return SWAP_AGAIN. This will allow shrink_page_list() -to recycle the page on the inactive list and hope that it has better luck -with the page next time. - -For file pages mapped into non-linear vmas, the try_to_munlock() logic works -slightly differently. On encountering a VM_LOCKED non-linear vma that might -map the page, try_to_munlock() returns SWAP_AGAIN without actually mlocking -the page. munlock_vma_page() will just leave the page unlocked and let -vmscan deal with it--the usual fallback position. - -Note that try_to_munlock()'s reverse map walk must visit every vma in a pages' -reverse map to determine that a page is NOT mapped into any VM_LOCKED vma. -However, the scan can terminate when it encounters a VM_LOCKED vma and can -successfully acquire the vma's mmap semphore for read and mlock the page. -Although try_to_munlock() can be called many [very many!] times when -munlock()ing a large region or tearing down a large address space that has been -mlocked via mlockall(), overall this is a fairly rare event. - -Mlocked Page: Page Reclaim in shrink_*_list() - -shrink_active_list() culls any obviously unevictable pages--i.e., -!page_evictable(page, NULL)--diverting these to the unevictable lru -list. However, shrink_active_list() only sees unevictable pages that -made it onto the active/inactive lru lists. Note that these pages do not -have PageUnevictable set--otherwise, they would be on the unevictable list and -shrink_active_list would never see them. +If try_to_unmap() is unable to acquire a VM_LOCKED VMA's associated mmap +semaphore, it will return SWAP_AGAIN. This will allow shrink_page_list() to +recycle the page on the inactive list and hope that it has better luck with the +page next time. + +For file pages mapped into non-linear VMAs, the try_to_munlock() logic works +slightly differently. On encountering a VM_LOCKED non-linear VMA that might +map the page, try_to_munlock() returns SWAP_AGAIN without actually mlocking the +page. munlock_vma_page() will just leave the page unlocked and let vmscan deal +with it - the usual fallback position. + +Note that try_to_munlock()'s reverse map walk must visit every VMA in a page's +reverse map to determine that a page is NOT mapped into any VM_LOCKED VMA. +However, the scan can terminate when it encounters a VM_LOCKED VMA and can +successfully acquire the VMA's mmap semphore for read and mlock the page. +Although try_to_munlock() might be called a great many times when munlocking a +large region or tearing down a large address space that has been mlocked via +mlockall(), overall this is a fairly rare event. + + +PAGE RECLAIM IN shrink_*_list() +------------------------------- + +shrink_active_list() culls any obviously unevictable pages - i.e. +!page_evictable(page, NULL) - diverting these to the unevictable list. +However, shrink_active_list() only sees unevictable pages that made it onto the +active/inactive lru lists. Note that these pages do not have PageUnevictable +set - otherwise they would be on the unevictable list and shrink_active_list +would never see them. Some examples of these unevictable pages on the LRU lists are: -1) ramfs pages that have been placed on the lru lists when first allocated. + (1) ramfs pages that have been placed on the LRU lists when first allocated. + + (2) SHM_LOCK'd shared memory pages. shmctl(SHM_LOCK) does not attempt to + allocate or fault in the pages in the shared memory region. This happens + when an application accesses the page the first time after SHM_LOCK'ing + the segment. -2) SHM_LOCKed shared memory pages. shmctl(SHM_LOCK) does not attempt to - allocate or fault in the pages in the shared memory region. This happens - when an application accesses the page the first time after SHM_LOCKing - the segment. + (3) mlocked pages that could not be isolated from the LRU and moved to the + unevictable list in mlock_vma_page(). -3) Mlocked pages that could not be isolated from the lru and moved to the - unevictable list in mlock_vma_page(). + (4) Pages mapped into multiple VM_LOCKED VMAs, but try_to_munlock() couldn't + acquire the VMA's mmap semaphore to test the flags and set PageMlocked. + munlock_vma_page() was forced to let the page back on to the normal LRU + list for vmscan to handle. -3) Pages mapped into multiple VM_LOCKED vmas, but try_to_munlock() couldn't - acquire the vma's mmap semaphore to test the flags and set PageMlocked. - munlock_vma_page() was forced to let the page back on to the normal - LRU list for vmscan to handle. +shrink_inactive_list() also diverts any unevictable pages that it finds on the +inactive lists to the appropriate zone's unevictable list. -shrink_inactive_list() also culls any unevictable pages that it finds on -the inactive lists, again diverting them to the appropriate zone's unevictable -lru list. shrink_inactive_list() should only see SHM_LOCKed pages that became -SHM_LOCKed after shrink_active_list() had moved them to the inactive list, or -pages mapped into VM_LOCKED vmas that munlock_vma_page() couldn't isolate from -the lru to recheck via try_to_munlock(). shrink_inactive_list() won't notice -the latter, but will pass on to shrink_page_list(). +shrink_inactive_list() should only see SHM_LOCK'd pages that became SHM_LOCK'd +after shrink_active_list() had moved them to the inactive list, or pages mapped +into VM_LOCKED VMAs that munlock_vma_page() couldn't isolate from the LRU to +recheck via try_to_munlock(). shrink_inactive_list() won't notice the latter, +but will pass on to shrink_page_list(). shrink_page_list() again culls obviously unevictable pages that it could encounter for similar reason to shrink_inactive_list(). Pages mapped into -VM_LOCKED vmas but without PG_mlocked set will make it all the way to +VM_LOCKED VMAs but without PG_mlocked set will make it all the way to try_to_unmap(). shrink_page_list() will divert them to the unevictable list when try_to_unmap() returns SWAP_MLOCK, as discussed above. |