linux-kernel - Re: [PATCH v3] mm/page_alloc: bail out on fatal signal during reclaim/compaction retry attempt

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Date:   Wed, 19 May 2021 21:34:55 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Aaron Tomlin <atomlin@...hat.com>
Cc:     linux-mm@...ck.org, vbabka@...e.cz, mhocko@...e.com,
        willy@...radead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mm/page_alloc: bail out on fatal signal during
 reclaim/compaction retry attempt

On Wed, 19 May 2021 21:17:43 +0100 Aaron Tomlin <atomlin@...hat.com> wrote:

> It does not make sense to retry compaction when a fatal signal is
> pending.

Well, it might make sense.  Presumably it is beneficial to other tasks.

> In the context of try_to_compact_pages(), indeed COMPACT_SKIPPED can be
> returned; albeit, not every zone, on the zone list, would be considered
> in the case a fatal signal is found to be pending.
> Yet, in should_compact_retry(), given the last known compaction result,
> each zone, on the zone list, can be considered/or checked
> (see compaction_zonelist_suitable()). For example, if a zone was found
> to succeed, then reclaim/compaction would be tried again
> (notwithstanding the above).
> 
> This patch ensures that compaction is not needlessly retried
> irrespective of the last known compaction result e.g. if it was skipped,
> in the unlikely case a fatal signal is found pending.
> So, OOM is at least attempted.

What observed problems motivated this change?

What were the observed runtime effects of this change?