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Subject: Re: [PATCH memcg] memcg: prohibit unconditional exceeding the limit
 of dying tasks
From:   Vasily Averin <vvs@virtuozzo.com>
To:     Michal Hocko <mhocko@kernel.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc:     cgroups@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <5b06a490-55bc-a6a0-6c85-690254f86fad@virtuozzo.com>
Message-ID: <8b98d44a-aeb2-5f5f-2545-ac2bd0c7049b@virtuozzo.com>
Date:   Mon, 13 Sep 2021 10:51:37 +0300
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On 9/10/21 3:39 PM, Vasily Averin wrote:
> The kernel currently allows dying tasks to exceed the memcg limits.
> The allocation is expected to be the last one and the occupied memory
> will be freed soon.
> This is not always true because it can be part of the huge vmalloc
> allocation. Allowed once, they will repeat over and over again.

> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 389b5766e74f..67195fcfbddf 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -2622,15 +2625,6 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask,
>  	if (gfp_mask & __GFP_ATOMIC)
>  		goto force;
>  
> -	/*
> -	 * Unlike in global OOM situations, memcg is not in a physical
> -	 * memory shortage.  Allow dying and OOM-killed tasks to
> -	 * bypass the last charges so that they can exit quickly and
> -	 * free their memory.
> -	 */
> -	if (unlikely(should_force_charge()))
> -		goto force;
> -

Should we keep current behaviour for (current->flags & PF_EXITING) case perhaps?
It is set inside do_exit only and (I hope) cannot trigger huge vmalloc allocations.

Thank you,
	Vasily Averin