Message-ID: <50253B95.7010905@jp.fujitsu.com>
Date: Sat, 11 Aug 2012 01:49:25 +0900
From: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
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To: Michal Hocko <mhocko@suse.cz>
CC: Glauber Costa <glommer@parallels.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, cgroups@vger.kernel.org, devel@openvz.org,
        Johannes Weiner <hannes@cmpxchg.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>, David Rientjes <rientjes@google.com>,
        Pekka Enberg <penberg@kernel.org>,
        Suleiman Souhlal <suleiman@google.com>
Subject: Re: [PATCH v2 02/11] memcg: Reclaim when more than one page needed.
References: <1344517279-30646-1-git-send-email-glommer@parallels.com> <1344517279-30646-3-git-send-email-glommer@parallels.com> <20120810154240.GG1425@dhcp22.suse.cz>
In-Reply-To: <20120810154240.GG1425@dhcp22.suse.cz>
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(2012/08/11 0:42), Michal Hocko wrote:
> On Thu 09-08-12 17:01:10, Glauber Costa wrote:
> [...]
>> @@ -2317,18 +2318,18 @@ static int mem_cgroup_do_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
>>   	} else
>>   		mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
>>   	/*
>> -	 * nr_pages can be either a huge page (HPAGE_PMD_NR), a batch
>> -	 * of regular pages (CHARGE_BATCH), or a single regular page (1).
>> -	 *
>>   	 * Never reclaim on behalf of optional batching, retry with a
>>   	 * single page instead.
>>   	 */
>> -	if (nr_pages == CHARGE_BATCH)
>> +	if (nr_pages > min_pages)
>>   		return CHARGE_RETRY;
>
> This is dangerous because THP charges will be retried now while they
> previously failed with CHARGE_NOMEM which means that we will keep
> attempting potentially endlessly.

with THP, I thought nr_pages == min_pages, and no retry.


> Why cannot we simply do if (nr_pages < CHARGE_BATCH) and get rid of the
> min_pages altogether?

Hm, I think a slab can be larger than CHARGE_BATCH.

> Also the comment doesn't seem to be valid anymore.
>
I agree it's not clean. Because our assumption on nr_pages are changed,
I think this behavior should not depend on nr_pages value..
Shouldn't we have a flag to indicate "trial-for-batched charge" ?


Thanks,
-Kame


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