linux-kernel - Re: [PATCH v4 0/3] Ignore non-LRU-based reclaim in memcg reclaim

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Message-Id: <20230405114841.248dffb65526383823c71d60@linux-foundation.org>
Date:   Wed, 5 Apr 2023 11:48:41 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Yosry Ahmed <yosryahmed@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Hyeonggon Yoo <42.hyeyoo@...il.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Miaohe Lin <linmiaohe@...wei.com>,
        David Hildenbrand <david@...hat.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Peter Xu <peterx@...hat.com>, NeilBrown <neilb@...e.de>,
        Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...nel.org>, Yu Zhao <yuzhao@...gle.com>,
        Dave Chinner <david@...morbit.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v4 0/3] Ignore non-LRU-based reclaim in memcg reclaim

On Tue, 4 Apr 2023 16:46:30 -0700 Yosry Ahmed <yosryahmed@...gle.com> wrote:

> > But the key question remains: how desirable is a backport?
> >
> > Looking at the changelogs I'm not seeing a clear statement of the
> > impact upon real-world users' real-world workloads.  (This is a hint).
> > So I am unable to judge.
> >
> > Please share your thoughts on this.
> 
> I think it's nice to have but not really important. It occasionally
> causes writes to memory.reclaim to report false positives and *might*
> cause unnecessary retrying when charging memory, but probably too rare
> to be a practical problem.
> 
> Personally, I intend to backport to our kernel at Google because it's
> a simple enough fix and we have occasionally seen test flakiness
> without it.
> 
> I have a reworked version of the series that only has 2 patches:
> - simple-two-liner-patch (actually 5 lines)
> - one patch including all refactoring squashed (introducing
> flush_reclaim_state() with the huge comment, introducing
> mm_account_reclaimed_pages(), and moving set_task_reclaim_state()
> around).
> 
> Let me know if you want me to send it as v5, or leave the current v4
> if you think backporting is not generally important.

Let's have a look at that v5 and see what people think?