linux-kernel - Re: Re: [RFC] [PATCH 9/9] memcg: percpu page cgroup lookup cache

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Date:	Thu, 11 Sep 2008 21:49:53 +0900 (JST)
From:	kamezawa.hiroyu@...fujitsu.com
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	balbir@...ux.vnet.ibm.com, xemul@...nvz.org, hugh@...itas.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, menage@...gle.com
Subject: Re: Re: [RFC] [PATCH 9/9] memcg: percpu page cgroup lookup cache

----- Original Message -----
>On Thursday 11 September 2008 21:24, KAMEZAWA Hiroyuki wrote:
>> Use per-cpu cache for fast access to page_cgroup.
>> This patch is for making fastpath faster.
>>
>> Because page_cgroup is accessed when the page is allocated/freed,
>> we can assume several of continuous page_cgroup will be accessed soon.
>> (If not interleaved on NUMA...but in such case, alloc/free itself is slow.)
>>
>> We cache some set of page_cgroup's base pointer on per-cpu area and
>> use it when we hit.
>>
>> TODO:
>>  - memory/cpu hotplug support.
>
>How much does this help?
>
1-2% in unixbench's test (in 0/9) on 2core/1socket x86-64/SMP host.
(cpu is not the newest one.)
This per-cpu covers 32 * 128MB=4GB of area.
Using 256 bytes(32 entry) is over-kill ?

Thanks,
-Kame
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