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Mon, 20 Jul 2026 10:42:23 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id qhMYMI/7XWpybAAAD6G6ig (envelope-from ); Mon, 20 Jul 2026 10:42:23 +0000 Date: Mon, 20 Jul 2026 12:42:18 +0200 From: David Sterba To: Usama Arif Cc: Andrew Morton , david@fromorbit.com, dgc@kernel.org, qi.zheng@linux.dev, baolin.wang@linux.alibaba.com, brauner@kernel.org, cgroups@vger.kernel.org, clm@fb.com, dsterba@suse.com, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@kernel.org, muchun.song@linux.dev, roman.gushchin@linux.dev, shakeel.butt@linux.dev, Al Viro , kernel-team@meta.com Subject: Re: [PATCH v2] fs: push nr_cached_objects memcg gating into individual filesystems Message-ID: <20260720104218.GA10684@twin.jikos.cz> Reply-To: dsterba@suse.cz References: <20260715103516.2410175-1-usama.arif@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260715103516.2410175-1-usama.arif@linux.dev> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) X-Rspamd-Action: no action X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: C5DE4180002 X-Rspam-User: X-Stat-Signature: gauadea7fmgkkyaoh566xnnsk5i7nuwk X-HE-Tag: 1784544145-586331 X-HE-Meta: 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 +ywvfScN Sq/HOpU1okpIv5lp3VKxBR8cnreT2O9VJ/chwfDktTsj1ge2xq6RDNM7gLvt4YI9tnSx+ibx/5FTdRVx+ApqV1vWs3I3TWcDuAR7iP0j2hLLRzpdrTHvk+AMmzNljEtILbFVcKEBdGl+wsq/QCRswSMz8tc4GsN3Pg30+QiYvA+wippnXHmSuWjGFJpavsgZt0TAmiRFv4t1/E5m3VXwSUh0X2++ZDKbLnoBH/8jutFWw6wjjPGbj3gqTi8vaya+0RWhi4SUKkWMsSr1GmfdsQRTCoct02Un76q0Qznufh0C3IDIVp0rhrx2S3ecQgro8n01zPFvD6L3Qs+BrQLKEtc+F5OXFjKCqmtj5M2il8ON9ZxTcZIvC/TOh5TpbOsLp53ST+MgIJPmNsxSSFLJR3lKl4Pmn5c07kgm6pUlt5hY8qUVICJwl8O+NisJjohcDEeNgTSTYhZTJzmptO5hbPoOAJYxrUmrbVF05O9zzmo/Lt/k= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Jul 15, 2026 at 03:35:16AM -0700, Usama Arif wrote: > Commit 0baad6f9b997 ("fs/super: skip non-memcg-aware nr_cached_objects > in memcg slab shrink") added a check in fs/super.c that skipped every > ->nr_cached_objects() hook whenever the shrinker was invoked for a > non-root memcg, on the assumption that none of them honour sc->memcg. > > That assumption is wrong for XFS, whose inode-reclaim hook is > intentionally driven from per-memcg contexts to free memcg-charged > slab. Encoding a blanket "never memcg-aware" policy in fs/super.c > short-circuits that path. > > Push the check down into the callbacks whose counters really are > irrelevant to per-memcg reclaim - btrfs_nr_cached_objects() and > shmem_unused_huge_count() - and drop the fs/super.c gate. Each > filesystem can now lift the restriction independently if its counter > later grows memcg awareness, without touching fs/super.c. > > Introduce mem_cgroup_shrink_is_root() in so the > callbacks don't open-code "sc->memcg is NULL or root". > > Fixes: 0baad6f9b997 ("fs/super: skip non-memcg-aware nr_cached_objects in memcg slab shrink") > Acked-by: Qi Zheng > Reviewed-by: Jan Kara > Reviewed-by: Shakeel Butt > Signed-off-by: Usama Arif > --- > v1 -> v2: > - Do not gate xfs_fs_nr_cached_objects(); XFS's inode reclaim is > intentionally driven from per-memcg contexts to free memcg-charged > slab (Dave Chinner). > - Add mem_cgroup_shrink_is_root() helper in so the > filesystem callbacks don't open-code "sc->memcg is NULL or root". > (Dave Chinner) > - Add fixes tag (Dave Chinner) > --- For > fs/btrfs/super.c | 10 ++++++++++ Acked-by: David Sterba Thanks.