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When we have a couple of hundred transactions on the fly at once, they all
typically modify the on disk superblock in some way.
create/unclink/mkdir/rmdir modify inode counts, allocation/freeing modify
free block counts.
When these counts are modified in a transaction, they must eventually lock
the superblock buffer and apply the mods. The buffer then remains locked
until the transaction is committed into the incore log buffer. The result
of this is that with enough transactions on the fly the incore superblock
buffer becomes a bottleneck.
The result of contention on the incore superblock buffer is that
transaction rates fall - the more pressure that is put on the superblock
buffer, the slower things go.
The key to removing the contention is to not require the superblock fields
in question to be locked. We do that by not marking the superblock dirty
in the transaction. IOWs, we modify the incore superblock but do not
modify the cached superblock buffer. In short, we do not log superblock
modifications to critical fields in the superblock on every transaction.
In fact we only do it just before we write the superblock to disk every
sync period or just before unmount.
This creates an interesting problem - if we don't log or write out the
fields in every transaction, then how do the values get recovered after a
crash? the answer is simple - we keep enough duplicate, logged information
in other structures that we can reconstruct the correct count after log
recovery has been performed.
It is the AGF and AGI structures that contain the duplicate information;
after recovery, we walk every AGI and AGF and sum their individual
counters to get the correct value, and we do a transaction into the log to
correct them. An optimisation of this is that if we have a clean unmount
record, we know the value in the superblock is correct, so we can avoid
the summation walk under normal conditions and so mount/recovery times do
not change under normal operation.
One wrinkle that was discovered during development was that the blocks
used in the freespace btrees are never accounted for in the AGF counters.
This was once a valid optimisation to make; when the filesystem is full,
the free space btrees are empty and consume no space. Hence when it
matters, the "accounting" is correct. But that means the when we do the
AGF summations, we would not have a correct count and xfs_check would
complain. Hence a new counter was added to track the number of blocks used
by the free space btrees. This is an *on-disk format change*.
As a result of this, lazy superblock counters are a mkfs option and at the
moment on linux there is no way to convert an old filesystem. This is
possible - xfs_db can be used to twiddle the right bits and then
xfs_repair will do the format conversion for you. Similarly, you can
convert backwards as well. At some point we'll add functionality to
xfs_admin to do the bit twiddling easily....
SGI-PV: 964999
SGI-Modid: xfs-linux-melb:xfs-kern:28652a
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Tim Shimmin <tes@sgi.com>
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SGI-PV: 963466
SGI-Modid: xfs-linux-melb:xfs-kern:28416a
Signed-off-by: Utako Kusaka <utako@tnes.nec.co.jp>
Signed-off-by: Tim Shimmin <tes@sgi.com>
Signed-off-by: Christoph Hellwig <hch@infradead.org>
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Patch provided by Eric Sandeen.
SGI-PV: 961695
SGI-Modid: xfs-linux-melb:xfs-kern:28205a
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>
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NULL.
Patch provided by Eric Sandeen.
SGI-PV: 961693
SGI-Modid: xfs-linux-melb:xfs-kern:28199a
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>
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After filesystem recovery the superblock is re-read to bring in any
changes. If the per-cpu superblock counters are not re-initialized from
the superblock then the next time the per-cpu counters are disabled they
might overwrite the global counter with a bogus value.
SGI-PV: 957348
SGI-Modid: xfs-linux-melb:xfs-kern:27999a
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>
Signed-off-by: David Chinner <dgc@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>
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Sandeen.
SGI-PV: 958736
SGI-Modid: xfs-linux-melb:xfs-kern:27596a
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>
Signed-off-by: Tim Shimmin <tes@sgi.com>
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warnings.
SGI-PV: 904196
SGI-Modid: xfs-linux-melb:xfs-kern:26364a
Signed-off-by: Nathan Scott <nathans@sgi.com>
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pure bloat.
SGI-PV: 952969
SGI-Modid: xfs-linux-melb:xfs-kern:26251a
Signed-off-by: Nathan Scott <nathans@sgi.com>
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interface.
SGI-PV: 953338
SGI-Modid: xfs-linux-melb:xfs-kern:26103a
Signed-off-by: Nathan Scott <nathans@sgi.com>
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shutdown vop flags consistent with sync vop flags declarations too.
SGI-PV: 939911
SGI-Modid: xfs-linux-melb:xfs-kern:26096a
Signed-off-by: Nathan Scott <nathans@sgi.com>
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logged version of di_next_unlinked which is actually always stored in the
correct ondisk format. This was pointed out to us by Shailendra Tripathi.
And is evident in the xfs qa test of 121.
SGI-PV: 953263
SGI-Modid: xfs-linux-melb:xfs-kern:26044a
Signed-off-by: Tim Shimmin <tes@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>
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64bit kernels allow recovery to handle both versions and do the necessary
decoding
SGI-PV: 952214
SGI-Modid: xfs-linux-melb:xfs-kern:26011a
Signed-off-by: Tim Shimmin <tes@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>
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these typos.
SGI-PV: 904196
SGI-Modid: xfs-linux-melb:xfs-kern:25539a
Signed-off-by: Nathan Scott <nathans@sgi.com>
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detected. Thanks to Roger Willcocks.
SGI-PV: 951054
SGI-Modid: xfs-linux-melb:xfs-kern:25477a
Signed-off-by: Nathan Scott <nathans@sgi.com>
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SGI-PV: 946444
SGI-Modid: xfs-linux-melb:xfs-kern:24768a
Signed-off-by: Nathan Scott <nathans@sgi.com>
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SGI-PV: 946611
SGI-Modid: xfs-linux-melb:xfs-kern:203307a
Signed-off-by: Eric Sandeen <sandeen@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>
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SGI-PV: 943272
SGI-Modid: xfs-linux:xfs-kern:201006a
Signed-off-by: Christoph Hellwig <hch@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>
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SGI-PV: 943272
SGI-Modid: xfs-linux:xfs-kern:199767a
Signed-off-by: Christoph Hellwig <hch@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>
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boilerplate.
SGI-PV: 913862
SGI-Modid: xfs-linux:xfs-kern:23903a
Signed-off-by: Nathan Scott <nathans@sgi.com>
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SGI-PV: 943122
SGI-Modid: xfs-linux:xfs-kern:23901a
Signed-off-by: Nathan Scott <nathans@sgi.com>
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/proc/mounts.
SGI-PV: 942984
SGI-Modid: xfs-linux:xfs-kern:23862a
Signed-off-by: Nathan Scott <nathans@sgi.com>
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<victor@cetuc.puc-rio.br>
SGI-PV: 940376
SGI-Modid: xfs-linux:xfs-kern:196705a
Signed-off-by: Christoph Hellwig <hch@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>
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SGI-PV: 938062
SGI-Modid: xfs-linux:xfs-kern:194415a
Signed-off-by: Christoph Hellwig <hch@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>
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SGI-PV: 932952
SGI-Modid: xfs-linux:xfs-kern:22805a
Signed-off-by: Nathan Scott <nathans@sgi.com>
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SGI-PV: 936255
SGI-Modid: xfs-linux:xfs-kern:192760a
Signed-off-by: Christoph Hellwig <hch@sgi.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>
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Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
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