[PATCH] XFS: Pagecache usage optimization on XFS

[Hisashi Hifumi]

Hi.

I introduced "is_partially_uptodate" aops for XFS.

A page can have multiple buffers and even if a page is not uptodate, some buffers 
can be uptodate on pagesize != blocksize environment.
This aops checks that all buffers which correspond to a part of a file 
that we want to read are uptodate. If so, we do not have to issue actual 
read IO to HDD even if a page is not uptodate because the portion we 
want to read are uptodate. 
"block_is_partially_uptodate" function is already used by ext2/3/4.
With the following patch random read/write mixed workloads or random read after 
random write workloads can be optimized and we can get performance improvement.

I did a performance test using the sysbench.

#sysbench --num-threads=4 --max-requests=100000 --test=fileio --file-num=1 
--file-block-size=8K --file-total-size=1G --file-test-mode=rndrw --file-fsync-freq=0 
--file-rw-ratio=0.5 run

-2.6.29-rc6
Test execution summary:
    total time:                          123.8645s
    total number of events:              100000
    total time taken by event execution: 442.4994
    per-request statistics:
         min:                            0.0000s
         avg:                            0.0044s
         max:                            0.3387s
         approx.  95 percentile:         0.0118s


-2.6.29-rc6-patched
Test execution summary:
    total time:                          108.0757s
    total number of events:              100000
    total time taken by event execution: 417.7505
    per-request statistics:
         min:                            0.0000s
         avg:                            0.0042s
         max:                            0.3217s
         approx.  95 percentile:         0.0118s


arch: ia64
pagesize: 16k
blocksize: 4k


Please merge following patch.
Thanks.

Signed-off-by: Hisashi Hifumi <hifumi.hisashi at oss.ntt.co.jp>

diff -Nrup linux-2.6.29-rc6.org/fs/xfs/linux-2.6/xfs_aops.c linux-2.6.29-rc6.xfs/fs/xfs/linux-2.6/xfs_aops.c
--- linux-2.6.29-rc6.org/fs/xfs/linux-2.6/xfs_aops.c	2009-03-02 09:26:08.000000000 +0900
+++ linux-2.6.29-rc6.xfs/fs/xfs/linux-2.6/xfs_aops.c	2009-03-04 10:26:21.000000000 +0900
@@ -1623,4 +1623,5 @@ const struct address_space_operations xf
 	.bmap			= xfs_vm_bmap,
 	.direct_IO		= xfs_vm_direct_IO,
 	.migratepage		= buffer_migrate_page,
+	.is_partially_uptodate  = block_is_partially_uptodate,
 };