From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-188.mta1.migadu.com (out-188.mta1.migadu.com [95.215.58.188]) (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 DD202346FB0 for ; Tue, 9 Jun 2026 12:30:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.188 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781008259; cv=none; b=hnnUIzwTgUDcz9iUabD71pkVpSEB8PgUWFPjUIDWCQDSMDZkTyo6S46++PLpPjr79mXNzI4s2zmCPGXYD3o2lyhSpO+coRS0kdOqir83fWrvcJRIote/nS24eIeIHlfysyOcW1pgzHs3P5hAiOgVTwF+jMBHdzK0NSveOqlqJXs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781008259; c=relaxed/simple; bh=nPG03SmqZwOcjX8/12Y3rN+1O64E3sALVV5t3j5yv6U=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=f/2VY21BjoBVty/LINqlDIXTXNAb1BvsP9EZxULJtWl8LDr4UeZhmWOH9g7jQVGy6aFzCLa0HIPRsufW15PMC/b6cBQuIU3qtSPvI3l+RR5WIllrbMsRRfc4xaggpnz3fK97imaMHeWyeJe7gGXt/wyyoijbDTXyp/oNTO6HCSk= 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=xL6tUdLv; arc=none smtp.client-ip=95.215.58.188 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="xL6tUdLv" 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=1781008254; 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=gSmhLbRZiCMLmvUSNQ09XQZBUjKHV+qKidrVgGQPtjM=; b=xL6tUdLvO6wGf/3x5Mz4uaE7Lf7/4EskVXo/P2dSlSfwoRuhGCMkji/5Y2L2/fQPurQWhF vjGt7pbV7bzOhX82Yj03E58N+R5IWqGcIM0UJL7FGy6s1Jb4gIrp6RYHf7nIsd3i19HxhV mjaJZlEr5mJaXetgmCzeJfrWRziwUbE= From: Usama Arif To: brauner@kernel.org, jack@suse.cz, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Al Viro , linux-mm@kvack.org Cc: hughd@google.com, boris@bur.io, clm@fb.com, dsterba@suse.com, linux-btrfs@vger.kernel.org, cem@kernel.org, linux-xfs@vger.kernel.org, shakeel.butt@linux.dev, hannes@cmpxchg.org, riel@surriel.com, kernel-team@meta.com, Usama Arif Subject: [PATCH] fs/super: skip non-memcg-aware nr_cached_objects in memcg slab shrink Date: Tue, 9 Jun 2026 05:30:47 -0700 Message-ID: <20260609123047.1948242-1-usama.arif@linux.dev> Precedence: bulk X-Mailing-List: linux-xfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT The super_block shrinker is registered with SHRINKER_MEMCG_AWARE because its dentry and inode LRUs are memcg-aware (via list_lru). But the optional ->nr_cached_objects() hooks that the shrinker also drives are not memcg-aware: btrfs extent maps and xfs inode reclaim operate on filesystem-global state, and shmem's unused-huge shrinker walks a per-superblock shrinklist. None of them filter by sc->memcg. The mismatch shows up under memcg-heavy slab reclaim. shrink_slab_memcg() calls do_shrink_slab() once per (memcg, NUMA node) pair for every memcg whose bit is set in the per-superblock shrinker bitmap, which on a busy host means hundreds of calls per reclaim pass. Each scan queues the same global shrinker work item that's already kicked from the root path. Because btrfs/xfs global count is typically non-zero on any in-use filesystem, the returned total stays positive even if a memcg's own dentry/inode LRUs are empty. shrink_slab_memcg() therefore never clears the SB shrinker bit in the memcg bitmap, so subsequent reclaim passes from the same memcg re-enter super_cache_count() and pay for the global counter walk again. Restrict ->nr_cached_objects() to the global shrink path (sc->memcg NULL or root). The memcg-aware dentry/inode LRUs keep being counted and scanned per memcg as before; only the global fs-specific hooks are skipped. The root/global shrink path still drives those hooks; only their invocation from non-root memcg slab reclaim is removed. Signed-off-by: Usama Arif --- fs/super.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) diff --git a/fs/super.c b/fs/super.c index 378e81efe643..5216c5dbd4c4 100644 --- a/fs/super.c +++ b/fs/super.c @@ -24,6 +24,7 @@ #include #include #include +#include #include #include #include /* for the emergency remount stuff */ @@ -169,6 +170,19 @@ 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. @@ -198,7 +212,7 @@ static unsigned long super_cache_scan(struct shrinker *shrink, if (!super_trylock_shared(sb)) return SHRINK_STOP; - if (sb->s_op->nr_cached_objects) + if (sb->s_op->nr_cached_objects && super_fs_objects_eligible(sc)) fs_objects = sb->s_op->nr_cached_objects(sb, sc); inodes = list_lru_shrink_count(&sb->s_inode_lru, sc); @@ -259,7 +273,8 @@ static unsigned long super_cache_count(struct shrinker *shrink, return 0; smp_rmb(); - if (sb->s_op && sb->s_op->nr_cached_objects) + if (sb->s_op && sb->s_op->nr_cached_objects && + super_fs_objects_eligible(sc)) total_objects = sb->s_op->nr_cached_objects(sb, sc); total_objects += list_lru_shrink_count(&sb->s_dentry_lru, sc); -- 2.52.0