linux-kernel - Re: [PATCH v5 01/14] memcg: Make it possible to use the stock for more than one page.

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Message-ID: <50803433.4000904@parallels.com>
Date:	Thu, 18 Oct 2012 20:54:11 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	<linux-mm@...ck.org>, <cgroups@...r.kernel.org>,
	Mel Gorman <mgorman@...e.de>, Tejun Heo <tj@...nel.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	<kamezawa.hiroyu@...fujitsu.com>, Christoph Lameter <cl@...ux.com>,
	David Rientjes <rientjes@...gle.com>,
	"Pekka Enberg" <penberg@...nel.org>, <devel@...nvz.org>,
	<linux-kernel@...r.kernel.org>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [PATCH v5 01/14] memcg: Make it possible to use the stock for
 more than one page.

On 10/18/2012 02:11 AM, Andrew Morton wrote:
> On Tue, 16 Oct 2012 14:16:38 +0400
> Glauber Costa <glommer@...allels.com> wrote:
> 
>> From: Suleiman Souhlal <ssouhlal@...eBSD.org>
>>
>> We currently have a percpu stock cache scheme that charges one page at a
>> time from memcg->res, the user counter. When the kernel memory
>> controller comes into play, we'll need to charge more than that.
>>
>> This is because kernel memory allocations will also draw from the user
>> counter, and can be bigger than a single page, as it is the case with
>> the stack (usually 2 pages) or some higher order slabs.
>>
>> ...
>>
>> -/*
>> - * Try to consume stocked charge on this cpu. If success, one page is consumed
>> - * from local stock and true is returned. If the stock is 0 or charges from a
>> - * cgroup which is not current target, returns false. This stock will be
>> - * refilled.
>> +/**
>> + * consume_stock: Try to consume stocked charge on this cpu.
>> + * @memcg: memcg to consume from.
>> + * @nr_pages: how many pages to charge.
>> + *
>> + * The charges will only happen if @memcg matches the current cpu's memcg
>> + * stock, and at least @nr_pages are available in that stock.  Failure to
>> + * service an allocation will refill the stock.
>> + *
>> + * returns true if succesfull, false otherwise.
> 
> spello.
> 
Thanks. I can never successfuly write successfull =(

>>   */
>> -static bool consume_stock(struct mem_cgroup *memcg)
>> +static bool consume_stock(struct mem_cgroup *memcg, int nr_pages)
> 
> I don't believe there is a case for nr_pages < 0 here?  If not then I
> suggest that it would be clearer to use an unsigned type, like
> memcg_stock_pcp.stock.
> 

Done, thanks.

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