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Diffstat (limited to 'Documentation/vm/numa')
| -rw-r--r-- | Documentation/vm/numa | 41 |
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diff --git a/Documentation/vm/numa b/Documentation/vm/numa new file mode 100644 index 00000000000..4b8db1bd3b7 --- /dev/null +++ b/Documentation/vm/numa @@ -0,0 +1,41 @@ +Started Nov 1999 by Kanoj Sarcar <kanoj@sgi.com> + +The intent of this file is to have an uptodate, running commentary +from different people about NUMA specific code in the Linux vm. + +What is NUMA? It is an architecture where the memory access times +for different regions of memory from a given processor varies +according to the "distance" of the memory region from the processor. +Each region of memory to which access times are the same from any +cpu, is called a node. On such architectures, it is beneficial if +the kernel tries to minimize inter node communications. Schemes +for this range from kernel text and read-only data replication +across nodes, and trying to house all the data structures that +key components of the kernel need on memory on that node. + +Currently, all the numa support is to provide efficient handling +of widely discontiguous physical memory, so architectures which +are not NUMA but can have huge holes in the physical address space +can use the same code. All this code is bracketed by CONFIG_DISCONTIGMEM. + +The initial port includes NUMAizing the bootmem allocator code by +encapsulating all the pieces of information into a bootmem_data_t +structure. Node specific calls have been added to the allocator. +In theory, any platform which uses the bootmem allocator should +be able to to put the bootmem and mem_map data structures anywhere +it deems best. + +Each node's page allocation data structures have also been encapsulated +into a pg_data_t. The bootmem_data_t is just one part of this. To +make the code look uniform between NUMA and regular UMA platforms, +UMA platforms have a statically allocated pg_data_t too (contig_page_data). +For the sake of uniformity, the function num_online_nodes() is also defined +for all platforms. As we run benchmarks, we might decide to NUMAize +more variables like low_on_memory, nr_free_pages etc into the pg_data_t. + +The NUMA aware page allocation code currently tries to allocate pages +from different nodes in a round robin manner. This will be changed to +do concentratic circle search, starting from current node, once the +NUMA port achieves more maturity. The call alloc_pages_node has been +added, so that drivers can make the call and not worry about whether +it is running on a NUMA or UMA platform. |