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

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Date:   Wed, 19 May 2021 20:08:01 +0100
From:   Aaron Tomlin <atomlin@...hat.com>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org, mhocko@...e.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_alloc: bail out on fatal signal during
 reclaim/compaction retry attempt

On Wed 2021-05-19 17:22 +0200, Vlastimil Babka wrote:
> Hm, indeed, if fatal_signal_pending() is true then try_to_compact_pages() will
> bail out in the for-each-zone loop after trying a single zone and if that zone
> keeps returning COMPACT_SKIPPED, things can get stuck.
> And direct reclaim might see compaction_ready() for another zone and return 1,
> faking the progress.

Indeed.

> So your patch seems to be solving the issue. But maybe we should just do the
> test at the beginning of should_compact_retry() and not specific to
> compaction_needs_reclaim() - if there's a fatal signal, there will be no
> compaction happening, so we should just say not to retry.

Fair enough - I will post a v2.

> I suppose if the patch fixes your situation where fatal_signal_pending() was
> true, there's hopefully not a more general problem with the retry logic?

At the present time, not to my knowledge. That being said, I will continue
to review the relevant source code further.



Kind regards,

-- 
Aaron Tomlin

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