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Date: Wed, 20 Jun 2012 23:36:47 +0400
From: Glauber Costa <glommer@parallels.com>
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To: Michal Hocko <mhocko@suse.cz>
CC: <linux-mm@kvack.org>, Pekka Enberg <penberg@kernel.org>,
        Cristoph Lameter <cl@linux.com>, David Rientjes <rientjes@google.com>,
        <cgroups@vger.kernel.org>, <devel@openvz.org>,
        <kamezawa.hiroyu@jp.fujitsu.com>, <linux-kernel@vger.kernel.org>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Suleiman Souhlal <suleiman@google.com>
Subject: Re: [PATCH v4 06/25] memcg: Make it possible to use the stock for
 more than one page.
References: <1340015298-14133-1-git-send-email-glommer@parallels.com> <1340015298-14133-7-git-send-email-glommer@parallels.com> <20120620132804.GF5541@tiehlicka.suse.cz>
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On 06/20/2012 05:28 PM, Michal Hocko wrote:
> On Mon 18-06-12 14:27:59, Glauber Costa wrote:
>> From: Suleiman Souhlal <ssouhlal@FreeBSD.org>
>>
>> Signed-off-by: Suleiman Souhlal <suleiman@google.com>
>> Signed-off-by: Glauber Costa <glommer@parallels.com>
>> Acked-by: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>
> I am not sure the patch is good to merge on its own without the rest.
> One comment bellow.
>
>> ---
>>   mm/memcontrol.c |   18 +++++++++---------
>>   1 file changed, 9 insertions(+), 9 deletions(-)
>>
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index ce15be4..00b9f1e 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -1998,19 +1998,19 @@ static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
>>   static DEFINE_MUTEX(percpu_charge_mutex);
>>
>>   /*
>> - * 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.
>> + * Try to consume stocked charge on this cpu. If success, nr_pages pages are
>> + * 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.
>>    */
>> -static bool consume_stock(struct mem_cgroup *memcg)
>> +static bool consume_stock(struct mem_cgroup *memcg, int nr_pages)
>>   {
>>   	struct memcg_stock_pcp *stock;
>>   	bool ret = true;
>
> I guess you want:
> 	if (nr_pages > CHARGE_BATCH)
> 		return false;
>
> because you don't want to try to use stock for THP pages.


The code reads:

+       if (memcg == stock->cached && stock->nr_pages >= nr_pages)
+               stock->nr_pages -= nr_pages;

Isn't stock->nr_pages always <= CHARGE_BATCH by definition?