linux-kernel - Re: [PATCH] memcg: fix memory.high target

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Message-ID: <20151124163857.GL29472@dhcp22.suse.cz>
Date:	Tue, 24 Nov 2015 17:38:58 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Vladimir Davydov <vdavydov@...tuozzo.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <tj@...nel.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memcg: fix memory.high target

On Mon 23-11-15 15:22:31, Vladimir Davydov wrote:
> When the memory.high threshold is exceeded, try_charge() schedules a
> task_work to reclaim the excess. The reclaim target is set to the number
> of pages requested by try_charge(). This is wrong, because try_charge()
> usually charges more pages than requested (batch > nr_pages) in order to
> refill per cpu stocks. As a result, a process in a cgroup can easily
> exceed memory.high significantly when doing a lot of charges w/o
> returning to userspace (e.g. reading a file in big chunks).
> 
> Fix this issue by assuring that when exceeding memory.high a process
> reclaims as many pages as were actually charged (i.e. batch).

Good point. This will not affect the single page load because the
reclaim is done in SWAP_CLUSTER_MAX chunks anyway.

> Signed-off-by: Vladimir Davydov <vdavydov@...tuozzo.com>

Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/memcontrol.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 648cc9f02437..06c476ab0f2c 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2133,7 +2133,7 @@ done_restock:
>  	 */
>  	do {
>  		if (page_counter_read(&memcg->memory) > memcg->high) {
> -			current->memcg_nr_pages_over_high += nr_pages;
> +			current->memcg_nr_pages_over_high += batch;
>  			set_notify_resume(current);
>  			break;
>  		}
> -- 
> 2.1.4

-- 
Michal Hocko
SUSE Labs
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