linux-kernel - Re: [PATCH] mm/page_alloc: try oom if reclaim is unable to make forward progress

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Date:   Fri, 19 Mar 2021 17:29:01 +0000
From:   Aaron Tomlin <atomlin@...hat.com>
To:     Michal Hocko <mhocko@...e.com>
Cc:     linux-mm@...ck.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/page_alloc: try oom if reclaim is unable to make
 forward progress

Hi Michal,

On Thu 2021-03-18 17:16 +0100, Michal Hocko wrote:
> On Mon 15-03-21 16:58:37, Aaron Tomlin wrote:
> > In the situation where direct reclaim is required to make progress for
> > compaction but no_progress_loops is already over the limit of
> > MAX_RECLAIM_RETRIES consider invoking the oom killer.

Firstly, thank you for your response.

> What is the problem you are trying to fix?

If I understand correctly, in the case of a "costly" order allocation
request that is permitted to repeatedly retry, it is possible to exceed the
maximum reclaim retry threshold as long as "some" progress is being made
even at the highest compaction priority. Furthermore, if the allocator has
a fatal signal pending, this is not considered.

In my opinion, it might be better to just give up straight away or try and
use the OOM killer only in the non-costly order allocation scenario to
assit reclaim. Looking at __alloc_pages_may_oom() the current logic is to
entirely skip the OOM killer for a costly order request, which makes sense.

Regards,

-- 
Aaron Tomlin