linux-kernel - Re: [PATCH 02/11] memcg: Reclaim when more than one page needed.

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Date:	Thu, 28 Jun 2012 00:47:24 +0400
From:	Glauber Costa <glommer@...allels.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	<cgroups@...r.kernel.org>, <linux-mm@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	<linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Pekka Enberg <penberg@...nel.org>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Christoph Lameter <cl@...ux.com>, <devel@...nvz.org>,
	<kamezawa.hiroyu@...fujitsu.com>, Tejun Heo <tj@...nel.org>,
	Suleiman Souhlal <suleiman@...gle.com>
Subject: Re: [PATCH 02/11] memcg: Reclaim when more than one page needed.

On 06/27/2012 11:48 PM, David Rientjes wrote:
> On Wed, 27 Jun 2012, Glauber Costa wrote:
> 
>>> @@ -2206,7 +2214,7 @@ static int mem_cgroup_do_charge(struct mem_cgroup
>>> *memcg, gfp_t gfp_mask,
>>>>  	 * unlikely to succeed so close to the limit, and we fall back
>>>>  	 * to regular pages anyway in case of failure.
>>>>  	 */
>>>> -	if (nr_pages == 1 && ret)
>>>> +	if (nr_pages <= NR_PAGES_TO_RETRY && ret)
>>>>  		return CHARGE_RETRY;
>>
>> Changed to costly order.
>>
> 
> 1 << PAGE_ALLOC_COSTLY_ORDER was the suggestion.

That is what I meant - to the costly order suggestion - , should have
been more explicit.

>> One more thing. The original version of this patch included
>> a cond_resched() here, that was also removed. From my re-reading
>> of the code in page_alloc.c and vmscan.c now, I tend to think
>> this is indeed not needed, since any cond_resched()s that might
>> be needed to ensure the safety of the code will be properly
>> inserted by the reclaim code itself, so there is no need for us
>> to include any when we signal that a retry is needed.
>>
> 
> For __GFP_WAIT, that sounds like a safe guarantee.
> 


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