linux-kernel - Re: [PATCH mmotm] memcg use generic percpu allocator instead of private one

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Date:	Thu, 21 Jan 2010 11:07:59 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	kirill@...temov.name
Subject: Re: [PATCH mmotm] memcg use generic percpu allocator instead of
 private one

On Wed, 20 Jan 2010 15:07:52 +0530
Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:
 
> > This includes no functional changes.
> > 
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> 
> 
> Before review, could you please post parallel pagefault data on a large
> system, since root now uses these per cpu counters and its overhead is
> now dependent on these counters. Also the data read from root cgroup is
> also dependent on these, could you make sure that is not broken.
> 
Hmm, I rewrote test program for avoidng mmap_sem. This version does fork()
instead of pthread_create() and meausre parallel-process page fault speed.

[Before patch]
[root@...extal memory]# /root/bin/perf stat -e page-faults,cache-misses --repeat 5 ./multi-fault-fork 8

 Performance counter stats for './multi-fault-fork 8' (5 runs):

       45256919  page-faults                ( +-   0.851% )
      602230144  cache-misses               ( +-   0.187% )

   61.020533723  seconds time elapsed   ( +-   0.002% 

[After patch]
[root@...extal memory]# /root/bin/perf stat -e page-faults,cache-misses --repeat 5 ./multi-fault-fork 8

 Performance counter stats for './multi-fault-fork 8' (5 runs):

       46007166  page-faults                ( +-   0.339% )
      599553505  cache-misses               ( +-   0.298% )

   61.020937843  seconds time elapsed   ( +-   0.004% )

slightly improved ? But this test program does some extreme behavior and
you can't see difference in real-world applications, I think.
So, I guess this is in error-range in famous (not small) benchmarks.

Thanks,
-Kame

View attachment "multi-fault-fork.c" of type "text/x-csrc" (1456 bytes)