(2012/12/26 2:22), Sha Zhengju wrote:

From: Sha Zhengju <redacted>

Commit a8e7d49a(Fix race in create_empty_buffers() vs __set_page_dirty_buffers())
extracts TestSetPageDirty from __set_page_dirty and is far away from
account_page_dirtied. But it's better to make the two operations in one single
function to keep modular. So in order to avoid the potential race mentioned in
commit a8e7d49a, we can hold private_lock until __set_page_dirty completes.
There's no deadlock between ->private_lock and ->tree_lock after confirmation.
It's a prepare patch for following memcg dirty page accounting patches.


Here is some test numbers that before/after this patch:
Test steps(Mem-4g, ext4):
drop_cache; sync
fio (ioengine=sync/write/buffered/bs=4k/size=1g/numjobs=2/group_reporting/thread)

We test it for 10 times and get the average numbers:
Before:
write: io=2048.0MB, bw=254117KB/s, iops=63528.9 , runt=  8279msec
lat (usec): min=1 , max=742361 , avg=30.918, stdev=1601.02
After:
write: io=2048.0MB, bw=254044KB/s, iops=63510.3 , runt=  8274.4msec
lat (usec): min=1 , max=856333 , avg=31.043, stdev=1769.32

Note that the impact is little(<1%).


Signed-off-by: Sha Zhengju <redacted>
Reviewed-by: Michal Hocko <redacted>

Acked-by: KAMEZAWA Hiroyuki <redacted>

Hmm,..this change should be double-checked by vfs, I/O guys...

increasing hold time of mapping->private_lock doesn't affect performance ?


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