Re: [patch 3/5] mm: try to distribute dirty pages fairly across zones

[Wu Fengguang <fengguang.wu@xxxxxxxxx>]

> //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@xxxxxxxxx>

Thanks,
Fengguang