linux-kernel - Re: [patch v2] mm, memcg: do not retry precharge charges

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Date:   Fri, 13 Jan 2017 09:40:14 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [patch v2] mm, memcg: do not retry precharge charges

On Thu 12-01-17 14:46:34, David Rientjes wrote:
> When memory.move_charge_at_immigrate is enabled and precharges are
> depleted during move, mem_cgroup_move_charge_pte_range() will attempt to
> increase the size of the precharge.
> 
> This can be allowed to do reclaim, but should not call the oom killer to
> oom kill a process.  It's better to fail the attach rather than oom kill
> a process attached to the memcg hierarchy.

This is not the case though since 3812c8c8f395 ("mm: memcg: do not trap
chargers with full callstack on OOM") - 3.12. Only the page fault path
is allowed to trigger the oom killer. 

> Prevent precharges from ever looping by setting __GFP_NORETRY.  This was
> probably the intention of the GFP_KERNEL & ~__GFP_NORETRY, which is
> pointless as written.
> 
> Fixes: 0029e19ebf84 ("mm: memcontrol: remove explicit OOM parameter in charge path")
> Signed-off-by: David Rientjes <rientjes@...gle.com>

Without the note about the oom killer you can add
Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!

> ---
>  mm/memcontrol.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4353,9 +4353,12 @@ static int mem_cgroup_do_precharge(unsigned long count)
>  		return ret;
>  	}
>  
> -	/* Try charges one by one with reclaim */
> +	/*
> +	 * Try charges one by one with reclaim, but do not retry.  This avoids
> +	 * calling the oom killer when the precharge should just fail.
> +	 */
>  	while (count--) {
> -		ret = try_charge(mc.to, GFP_KERNEL & ~__GFP_NORETRY, 1);
> +		ret = try_charge(mc.to, GFP_KERNEL | __GFP_NORETRY, 1);
>  		if (ret)
>  			return ret;
>  		mc.precharge++;

-- 
Michal Hocko
SUSE Labs