linux-kernel - Re: [PATCH] fs, mm: account filp and names caches to kmemcg

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Date:   Tue, 24 Oct 2017 14:18:59 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Greg Thelen <gthelen@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>
Cc:     Shakeel Butt <shakeelb@...gle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>, linux-fsdevel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs, mm: account filp and names caches to kmemcg

Does this sound something that you would be interested in? I can spend
som more time on it if it is worthwhile.

On Fri 13-10-17 17:24:21, Michal Hocko wrote:
> Well, it actually occured to me that this would trigger the global oom
> killer in case no memcg specific victim can be found which is definitely
> not something we would like to do. This should work better. I am not
> sure we can trigger this corner case but we should cover it and it
> actually doesn't make the code much worse.
> ---
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index d5f3a62887cf..7b370f070b82 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1528,26 +1528,40 @@ static void memcg_oom_recover(struct mem_cgroup *memcg)
>  
>  static void mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int order)
>  {
> -	if (!current->memcg_may_oom)
> -		return;
>  	/*
>  	 * We are in the middle of the charge context here, so we
>  	 * don't want to block when potentially sitting on a callstack
>  	 * that holds all kinds of filesystem and mm locks.
>  	 *
> -	 * Also, the caller may handle a failed allocation gracefully
> -	 * (like optional page cache readahead) and so an OOM killer
> -	 * invocation might not even be necessary.
> +	 * cgroup v1 allowes sync users space handling so we cannot afford
> +	 * to get stuck here for that configuration. That's why we don't do
> +	 * anything here except remember the OOM context and then deal with
> +	 * it at the end of the page fault when the stack is unwound, the
> +	 * locks are released, and when we know whether the fault was overall
> +	 * successful.
> +	 *
> +	 * On the other hand, in-kernel OOM killer allows for an async victim
> +	 * memory reclaim (oom_reaper) and that means that we are not solely
> +	 * relying on the oom victim to make a forward progress so we can stay
> +	 * in the the try_charge context and keep retrying as long as there
> +	 * are oom victims to select.
>  	 *
> -	 * That's why we don't do anything here except remember the
> -	 * OOM context and then deal with it at the end of the page
> -	 * fault when the stack is unwound, the locks are released,
> -	 * and when we know whether the fault was overall successful.
> +	 * Please note that mem_cgroup_oom_synchronize might fail to find a
> +	 * victim and then we have rely on mem_cgroup_oom_synchronize otherwise
> +	 * we would fall back to the global oom killer in pagefault_out_of_memory
>  	 */
> +	if (!memcg->oom_kill_disable &&
> +			mem_cgroup_out_of_memory(memcg, mask, order))
> +		return true;
> +
> +	if (!current->memcg_may_oom)
> +		return false;
>  	css_get(&memcg->css);
>  	current->memcg_in_oom = memcg;
>  	current->memcg_oom_gfp_mask = mask;
>  	current->memcg_oom_order = order;
> +
> +	return false;
>  }
>  
>  /**
> @@ -2007,8 +2021,11 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
>  
>  	mem_cgroup_event(mem_over_limit, MEMCG_OOM);
>  
> -	mem_cgroup_oom(mem_over_limit, gfp_mask,
> -		       get_order(nr_pages * PAGE_SIZE));
> +	if (mem_cgroup_oom(mem_over_limit, gfp_mask,
> +		       get_order(nr_pages * PAGE_SIZE))) {
> +		nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
> +		goto retry;
> +	}
>  nomem:
>  	if (!(gfp_mask & __GFP_NOFAIL))
>  		return -ENOMEM;
> -- 
> Michal Hocko
> SUSE Labs

-- 
Michal Hocko
SUSE Labs