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SubjectRe: [patch 3/5] mm: try to distribute dirty pages fairly across zones
> //regression
> 3) much increased cpu %user and %system for btrfs

Sorry I find out that the CPU time regressions for btrfs are caused by
some additional trace events enabled on btrfs (for debugging an
unrelated btrfs hang bug) which results in 7 times more trace event
lines:

2701238 /export/writeback/thresh=1000M/btrfs-1dd-4k-8p-2941M-1000M:10-3.1.0-rc9-ioless-full-nfs-wq5-next-20111014+
19054054 /export/writeback/thresh=1000M/btrfs-1dd-4k-8p-2941M-1000M:10-3.1.0-rc9-ioless-full-per-zone-dirty-next-20111014+

So no real regressions.

Besides, the patchset also performs good on random writes:

3.1.0-rc9-ioless-full-nfs-wq5-next-20111014+ 3.1.0-rc9-ioless-full-per-zone-dirty-next-20111014+
------------------------ ------------------------
1.65 -5.1% 1.57 MMAP-RANDWRITE-4K/btrfs-fio_fat_mmap_randwrite_4k-4k-8p-4096M-20:10-X
18.65 -6.4% 17.46 MMAP-RANDWRITE-4K/ext3-fio_fat_mmap_randwrite_4k-4k-8p-4096M-20:10-X
2.09 +1.2% 2.12 MMAP-RANDWRITE-4K/ext4-fio_fat_mmap_randwrite_4k-4k-8p-4096M-20:10-X
2.49 -0.3% 2.48 MMAP-RANDWRITE-4K/xfs-fio_fat_mmap_randwrite_4k-4k-8p-4096M-20:10-X
51.35 +0.0% 51.36 MMAP-RANDWRITE-64K/btrfs-fio_fat_mmap_randwrite_64k-64k-8p-4096M-20:10-X
45.20 +0.5% 45.43 MMAP-RANDWRITE-64K/ext3-fio_fat_mmap_randwrite_64k-64k-8p-4096M-20:10-X
44.77 +0.7% 45.10 MMAP-RANDWRITE-64K/ext4-fio_fat_mmap_randwrite_64k-64k-8p-4096M-20:10-X
45.11 +2.5% 46.23 MMAP-RANDWRITE-64K/xfs-fio_fat_mmap_randwrite_64k-64k-8p-4096M-20:10-X
211.31 +0.2% 211.74 TOTAL write_bw

And writes to USB key:

3.1.0-rc9-ioless-full-nfs-wq5-next-20111014+ 3.1.0-rc9-ioless-full-per-zone-dirty-next-20111014+
------------------------ ------------------------
5.94 +0.8% 5.99 UKEY-thresh=1G/btrfs-1dd-4k-8p-4096M-1024M:10-X
2.64 -0.8% 2.62 UKEY-thresh=1G/ext3-10dd-4k-8p-4096M-1024M:10-X
5.10 +0.3% 5.12 UKEY-thresh=1G/ext3-1dd-4k-8p-4096M-1024M:10-X
3.26 -0.8% 3.24 UKEY-thresh=1G/ext3-2dd-4k-8p-4096M-1024M:10-X
5.63 -0.5% 5.60 UKEY-thresh=1G/ext4-10dd-4k-8p-4096M-1024M:10-X
6.04 -0.1% 6.04 UKEY-thresh=1G/ext4-1dd-4k-8p-4096M-1024M:10-X
5.90 -0.2% 5.88 UKEY-thresh=1G/ext4-2dd-4k-8p-4096M-1024M:10-X
2.45 +22.6% 3.00 UKEY-thresh=1G/xfs-10dd-4k-8p-4096M-1024M:10-X
6.18 -0.4% 6.16 UKEY-thresh=1G/xfs-1dd-4k-8p-4096M-1024M:10-X
4.81 +0.0% 4.81 UKEY-thresh=1G/xfs-2dd-4k-8p-4096M-1024M:10-X
47.94 +1.1% 48.45 TOTAL write_bw

In summary, I see no problem at all in these trivial writeback tests.

Tested-by: Wu Fengguang <fengguang.wu@intel.com>

Thanks,
Fengguang


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