linux-kernel - Re: [PATCH] memcg: simplify unreclaimable groups handling in soft limit reclaim

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Date:	Tue, 21 Oct 2014 10:10:09 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Vladimir Davydov <vdavydov@...allels.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] memcg: simplify unreclaimable groups handling in soft
 limit reclaim

On Mon 20-10-14 19:55:54, Vladimir Davydov wrote:
> If we fail to reclaim anything from a cgroup during a soft reclaim pass
> we want to get the next largest cgroup exceeding its soft limit. To
> achieve this, we should obviously remove the current group from the tree
> and then pick the largest group. Currently we have a weird loop instead.
> Let's simplify it.
> 
> Signed-off-by: Vladimir Davydov <vdavydov@...allels.com>

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

> ---
>  mm/memcontrol.c |   26 ++++----------------------
>  1 file changed, 4 insertions(+), 22 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e957f0c80c6e..53393e27ff03 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -3507,34 +3507,16 @@ unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
>  		nr_reclaimed += reclaimed;
>  		*total_scanned += nr_scanned;
>  		spin_lock_irq(&mctz->lock);
> +		__mem_cgroup_remove_exceeded(mz, mctz);
>  
>  		/*
>  		 * If we failed to reclaim anything from this memory cgroup
>  		 * it is time to move on to the next cgroup
>  		 */
>  		next_mz = NULL;
> -		if (!reclaimed) {
> -			do {
> -				/*
> -				 * Loop until we find yet another one.
> -				 *
> -				 * By the time we get the soft_limit lock
> -				 * again, someone might have aded the
> -				 * group back on the RB tree. Iterate to
> -				 * make sure we get a different mem.
> -				 * mem_cgroup_largest_soft_limit_node returns
> -				 * NULL if no other cgroup is present on
> -				 * the tree
> -				 */
> -				next_mz =
> -				__mem_cgroup_largest_soft_limit_node(mctz);
> -				if (next_mz == mz)
> -					css_put(&next_mz->memcg->css);
> -				else /* next_mz == NULL or other memcg */
> -					break;
> -			} while (1);
> -		}
> -		__mem_cgroup_remove_exceeded(mz, mctz);
> +		if (!reclaimed)
> +			next_mz = __mem_cgroup_largest_soft_limit_node(mctz);
> +
>  		excess = soft_limit_excess(mz->memcg);
>  		/*
>  		 * One school of thought says that we should not add
> -- 
> 1.7.10.4
> 

-- 
Michal Hocko
SUSE Labs
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