Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [patch] mm, oom: stop reclaiming if GFP_ATOMIC will start failing
 soon
To:     David Rientjes <rientjes@google.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Vlastimil Babka <vbabka@suse.cz>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
References: <alpine.DEB.2.22.394.2004241347310.70176@chino.kir.corp.google.com>
From:   Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Message-ID: <6ed3e585-394a-42ff-03c4-a9bb8b5fcbc4@I-love.SAKURA.ne.jp>
Date:   Sat, 25 Apr 2020 09:32:02 +0900
User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:68.0) Gecko/20100101
 Thunderbird/68.7.0
MIME-Version: 1.0
In-Reply-To: <alpine.DEB.2.22.394.2004241347310.70176@chino.kir.corp.google.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 2020/04/25 5:48, David Rientjes wrote:
> @@ -4372,11 +4372,21 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
>  					ac->nodemask) {
>  		unsigned long available;
>  		unsigned long reclaimable;
> +		unsigned long free;
>  		unsigned long min_wmark = min_wmark_pages(zone);
>  		bool wmark;
>  
> +		free = zone_page_state_snapshot(zone, NR_FREE_PAGES);
> +		/*
> +		 * If this zone is approaching the point where even order-0
> +		 * GFP_ATOMIC allocations will fail, stop considering reclaim.
> +		 */
> +		if (!__zone_watermark_ok(zone, 0, min_wmark, ac_classzone_idx(ac),
> +					 alloc_flags | ALLOC_HIGH, free))
> +			continue;

This is to trigger the OOM killer more aggressively, isn't it? But where is the
guarantee that this is an allocation request which can trigger the OOM killer?
If this is an allocation request which cannot trigger the OOM killer, wouldn't
this cause premature allocation failures?

> +
>  		available = reclaimable = zone_reclaimable_pages(zone);
> -		available += zone_page_state_snapshot(zone, NR_FREE_PAGES);
> +		available += free;
>  
>  		/*
>  		 * Would the allocation succeed if we reclaimed all
>