From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-171.mta0.migadu.com (out-171.mta0.migadu.com [91.218.175.171]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 412AB44211D for ; Wed, 15 Jul 2026 10:35:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784111740; cv=none; b=ObgSXA4ms7F7icIvaMwHBQMb/PxuIa1BkDJhGbdYDs4U7WxT6Rf+ZOD8Nbuyy/1WgUPZPeOsFrdOYDBS4/o08OWvRTjgIm9xUwbvW6mfD+jBT7bc+uvmLIPzLoIy/SaHEFxTyuMp7ggeLdBAZQi51ddLYhcdjBW32n7OgWZQTSw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784111740; c=relaxed/simple; bh=SwdezaImxQcMt43h0jRN9TZ6bt6yTKaTU02f07mkxsA=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=aV40SsjYD8kCCYOA/+iIU7RL1LcZrlvXCufUlU6k5X86u4J+jSWyPaCkfl2M5Ticg1tidZeqxNSXs1qsfrUeVx/65TfdgD/Rc+N7HaTms00gqkUkmrIHR3K1wpgKDnjF8o+Pe9MUsM1zUENajfvgt/07PVX+6E+t4CUTZ4a/TJ4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=lWVjevAk; arc=none smtp.client-ip=91.218.175.171 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="lWVjevAk" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1784111726; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=0PjHU3TbDnfGWF+iD96TKWS2XZ53YHp9da69Ponf0rw=; b=lWVjevAkYZ064aFltJs8lMrrHhbvW3jfDDXTJNUk7br0vYrO703lDuTQkLrrB6DW2oxclA CDTz4ntBIHKH7+v1OXbDtlB7q9AuF4Y9XDGtBTQ8/JYqvFRDPp3/uFjWpytuv6YlkxJ9HI zsJlgnUW59RhgT+41ErbmMD+ZA0Uy4k= From: Usama Arif To: 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 Cc: Usama Arif Subject: [PATCH v2] fs: push nr_cached_objects memcg gating into individual filesystems Date: Wed, 15 Jul 2026 03:35:16 -0700 Message-ID: <20260715103516.2410175-1-usama.arif@linux.dev> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT 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) --- fs/btrfs/super.c | 10 ++++++++++ fs/super.c | 19 ++----------------- include/linux/memcontrol.h | 21 +++++++++++++++++++++ mm/shmem.c | 10 ++++++++++ 4 files changed, 43 insertions(+), 17 deletions(-) diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c index a7d804219bec..cc4537435399 100644 --- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -22,6 +22,7 @@ #include #include #include +#include #include #include #include @@ -2434,6 +2435,15 @@ static long btrfs_nr_cached_objects(struct super_block *sb, struct shrink_contro struct btrfs_fs_info *fs_info = btrfs_sb(sb); const s64 nr = percpu_counter_read_positive(&fs_info->evictable_extent_maps); + /* + * The evictable extent map counter is filesystem-global and does not + * honour sc->memcg, so it is only meaningful on the global (kswapd or + * root direct reclaim) shrink path. Skip the per-memcg iterations of + * shrink_slab_memcg() to avoid queueing duplicate global work. + */ + if (!mem_cgroup_shrink_is_root(sc)) + return 0; + trace_btrfs_extent_map_shrinker_count(fs_info, nr); return nr; diff --git a/fs/super.c b/fs/super.c index d2d04a6f4f84..a8fd61136aaf 100644 --- a/fs/super.c +++ b/fs/super.c @@ -24,7 +24,6 @@ #include #include #include -#include #include #include #include /* for the emergency remount stuff */ @@ -170,19 +169,6 @@ static void super_wake(struct super_block *sb, unsigned int flag) wake_up_var(&sb->s_flags); } -/* - * The s_op->nr_cached_objects hooks (used for example by btrfs and xfs) - * operate on filesystem-global state and ignore sc->memcg. Driving them - * from per-memcg shrink_slab_memcg() invocations only burns CPU walking - * per-cpu counters and queueing duplicate work: the actual reclaim happens on - * the global path (kswapd or root direct reclaim) regardless. Restrict them - * to that path. - */ -static inline bool super_fs_objects_eligible(struct shrink_control *sc) -{ - return !sc->memcg || mem_cgroup_is_root(sc->memcg); -} - /* * One thing we have to be careful of with a per-sb shrinker is that we don't * drop the last active reference to the superblock from within the shrinker. @@ -212,7 +198,7 @@ static unsigned long super_cache_scan(struct shrinker *shrink, if (!super_trylock_shared(sb)) return SHRINK_STOP; - if (sb->s_op->nr_cached_objects && super_fs_objects_eligible(sc)) + if (sb->s_op->nr_cached_objects) fs_objects = sb->s_op->nr_cached_objects(sb, sc); inodes = list_lru_shrink_count(&sb->s_inode_lru, sc); @@ -273,8 +259,7 @@ static unsigned long super_cache_count(struct shrinker *shrink, return 0; smp_rmb(); - if (sb->s_op && sb->s_op->nr_cached_objects && - super_fs_objects_eligible(sc)) + if (sb->s_op && sb->s_op->nr_cached_objects) total_objects = sb->s_op->nr_cached_objects(sb, sc); total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc); diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index e1f46a0016fc..5407e4200460 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -520,6 +520,22 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg) return (memcg == root_mem_cgroup); } +/** + * mem_cgroup_shrink_is_root - is this a global or root-memcg shrink invocation? + * @sc: shrink_control describing the current shrinker call + * + * Returns true when @sc represents a global reclaim shrink (sc->memcg == NULL) + * or a root-memcg shrink, i.e. not a per-memcg iteration of + * shrink_slab_memcg(). Filesystems whose ->nr_cached_objects()/ + * ->free_cached_objects() implementations operate on filesystem-global state + * and do not honour sc->memcg can use this to early-return 0 in per-memcg + * contexts. + */ +static inline bool mem_cgroup_shrink_is_root(struct shrink_control *sc) +{ + return !sc->memcg || mem_cgroup_is_root(sc->memcg); +} + static inline bool obj_cgroup_is_root(const struct obj_cgroup *objcg) { return objcg->is_root; @@ -1071,6 +1087,11 @@ static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg) return true; } +static inline bool mem_cgroup_shrink_is_root(struct shrink_control *sc) +{ + return true; +} + static inline bool obj_cgroup_is_root(const struct obj_cgroup *objcg) { return true; diff --git a/mm/shmem.c b/mm/shmem.c index 5789a0f5a346..dc8cd4f563f4 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -846,6 +846,16 @@ static long shmem_unused_huge_count(struct super_block *sb, struct shrink_control *sc) { struct shmem_sb_info *sbinfo = SHMEM_SB(sb); + + /* + * The per-superblock shrinklist is filesystem-global and does not + * honour sc->memcg, so it is only meaningful on the global (kswapd or + * root direct reclaim) shrink path. Skip the per-memcg iterations of + * shrink_slab_memcg() to avoid queueing duplicate global work. + */ + if (!mem_cgroup_shrink_is_root(sc)) + return 0; + return READ_ONCE(sbinfo->shrinklist_len); } #else /* !CONFIG_TRANSPARENT_HUGEPAGE */ -- 2.53.0-Meta