linux-kernel - Re: [RFC][PATCH 4/5] memcg: per-cpu charge stock

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Message-ID: <b18a62cbada2801ab34d591ba65ef906.squirrel@webmail-b.css.fujitsu.com>
Date:	Mon, 31 Aug 2009 21:07:10 +0900 (JST)
From:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	"KAMEZAWA Hiroyuki" <kamezawa.hiroyu@...fujitsu.com>,
	"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>
Subject: Re: [RFC][PATCH 4/5] memcg: per-cpu charge stock

Balbir Singh wrote:
> * KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> [2009-08-28
> 13:27:06]:
>
>>
>> For avoiding frequent access to res_counter at charge, add per-cpu
>> local charge. Comparing with modifing res_coutner (with percpu_counter),
>> this approach
>> Pros.
>> 	- we don't have to touch res_counter's cache line
>> 	- we don't have to chase res_counter's hierarchy
>> 	- we don't have to call res_counter function.
>> Cons.
>> 	- we need our own code.
>>
>> Considering trade-off, I think this is worth to do.
>
> I prefer the other part due to
>
> 1. Code reuse (any enhancements made will benefit us)
> 2. Custom batching that can be done easily
> 3. Remember hierarchy is explicitly enabled and we've documented that
> it is expensive

Hmm. the important point is we don't touch res_counter's cacheline in
fast path. And if we don't use memcg's percpu counter, more cacheline/TLB
will be necesary. (I think percpu counter is slow.)
plz rewrite memcg's percpu counter by youself if you want something generic.

I can't understand what you mention by (3).

Thanks,
-Kame


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