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

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Date:   Tue, 28 Feb 2023 08:50:00 +0000
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,
        Yosry Ahmed <yosryahmed@...gle.com>
Subject: [PATCH v1 0/2] Ignore non-LRU-based reclaim in memcg reclaim

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