linux-kernel - Re: [PATCH v1 0/2] Ignore non-LRU-based reclaim in memcg reclaim

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Message-ID: <CAJD7tkbjidNgKi1RLOyVks-RR34mXh+QkKf_BZY_ZcMrjfP0TQ@mail.gmail.com>
Date:   Tue, 7 Mar 2023 22:54:44 -0800
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     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>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1 0/2] Ignore non-LRU-based reclaim in memcg reclaim

On Tue, Feb 28, 2023 at 12:50 AM Yosry Ahmed <yosryahmed@...gle.com> wrote:
>
> Reclaimed pages through other means than LRU-based reclaim are tracked
> through reclaim_state in struct scan_control, which is stashed in
> current task_struct. These pages are added to the number of reclaimed
> pages through LRUs. For memcg reclaim, these pages generally cannot be
> linked to the memcg under reclaim and can cause an overestimated count
> of reclaimed pages. This short series tries to address that.
>
> Patch 1 is just refactoring updating reclaim_state into a helper
> function, and renames reclaimed_slab to just reclaimed, with a comment
> describing its true purpose.
>
> Patch 2 ignores pages reclaimed outside of LRU reclaim in memcg reclaim.
> The pages are uncharged anyway, so even if we end up under-reporting
> reclaimed pages we will still succeed in making progress during
> charging.
>
> Do not let the diff stat trick you, patch 2 is a one-line change. All
> the rest is moving a couple of functions around and a huge comment :)
>
> RFC -> v1:
> - Exported report_freed_pages in case XFS is built as a module (Matthew
>   Wilcox).
> - Renamed reclaimed_slab to reclaim in previously missed MGLRU code.
> - Refactored using reclaim_state to update sc->nr_reclaimed into a
>   helper and added an XL comment explaining why we ignore
>   reclaim_state->reclaimed in memcg reclaim (Johannes Weiner).
>
> Yosry Ahmed (2):
>   mm: vmscan: refactor updating reclaimed pages in reclaim_state
>   mm: vmscan: ignore non-LRU-based reclaim in memcg reclaim
>
>  fs/inode.c           |  3 +-
>  fs/xfs/xfs_buf.c     |  3 +-
>  include/linux/swap.h |  5 ++-
>  mm/slab.c            |  3 +-
>  mm/slob.c            |  6 ++--
>  mm/slub.c            |  5 ++-
>  mm/vmscan.c          | 79 +++++++++++++++++++++++++++++++++++---------
>  7 files changed, 74 insertions(+), 30 deletions(-)
>
> --
> 2.39.2.722.g9855ee24e9-goog
>

Friendly ping on this series, any comments or thoughts -- especially
on the memcg side?