linux-kernel - Re: [PATCH V3 2/8] Make TestSetPageDirty and dirty page accounting in one func

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Date:	Fri, 28 Dec 2012 09:39:25 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Sha Zhengju <handai.szj@...il.com>
CC:	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	dchinner@...hat.com, mhocko@...e.cz, akpm@...ux-foundation.org,
	gthelen@...gle.com, fengguang.wu@...el.com, glommer@...allels.com,
	Sha Zhengju <handai.szj@...bao.com>
Subject: Re: [PATCH V3 2/8] Make TestSetPageDirty and dirty page accounting
 in one func

(2012/12/26 2:22), Sha Zhengju wrote:
> From: Sha Zhengju <handai.szj@...bao.com>
> 
> 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 <handai.szj@...bao.com>
> Reviewed-by: Michal Hocko <mhocko@...e.cz>

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

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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