linux-kernel - Re: [PATCH v4] mm/page_alloc: bail out on fatal signal during reclaim/compaction retry attempt

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Message-ID: <c7b69523-c141-d06c-bc02-953c7a939d91@suse.cz>
Date:   Mon, 31 May 2021 13:35:31 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Michal Hocko <mhocko@...e.com>, Aaron Tomlin <atomlin@...hat.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org, willy@...radead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] mm/page_alloc: bail out on fatal signal during
 reclaim/compaction retry attempt

On 5/31/21 1:33 PM, Michal Hocko wrote:
> On Thu 20-05-21 15:29:01, Aaron Tomlin wrote:
>> A customer experienced a low-memory situation and decided to issue a
>> SIGKILL (i.e. a fatal signal). Instead of promptly terminating as one
>> would expect, the aforementioned task remained unresponsive.
>> 
>> Further investigation indicated that the task was "stuck" in the
>> reclaim/compaction retry loop. Now, it does not make sense to retry
>> compaction when a fatal signal is pending.
> 
> Is this really true in general? The memory reclaim is retried even when
> fatal signals are pending. Why should be compaction different? I do
> agree that retrying way too much is bad but is there any reason why this
> special case doesn't follow the max retry logic?

Compaction doesn't do anything if fatal signal is pending, it bails out
immediately and the checks are rather frequent. So why retry?