From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3ED50C5AD4E for ; Mon, 10 Aug 2026 10:20:07 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 10B026B0098; Mon, 10 Aug 2026 06:20:06 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0E3086B0099; Mon, 10 Aug 2026 06:20:06 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 01F9C6B009B; Mon, 10 Aug 2026 06:20:05 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id CC7596B0098 for ; Mon, 10 Aug 2026 06:20:05 -0400 (EDT) Received: from smtpin22.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 7341040555 for ; Mon, 10 Aug 2026 10:20:05 +0000 (UTC) X-FDA: 85084964370.22.571F60E Received: from out-180.mta0.migadu.com (out-180.mta0.migadu.com [91.218.175.180]) by imf21.hostedemail.com (Postfix) with ESMTP id 8B2C21C0007 for ; Mon, 10 Aug 2026 10:20:03 +0000 (UTC) Authentication-Results: imf21.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=fGXDlnyO; spf=pass (imf21.hostedemail.com: domain of usama.arif@linux.dev designates 91.218.175.180 as permitted sender) smtp.mailfrom=usama.arif@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1786357203; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=2kxNcoz88gUTv2RyDdUD2oJ4g9y+1zQ1kNSN4EE2fzA=; b=hrT7e06ozSvyDifRumOa8mReEo4Jnf5bkZjLYZt+9l2N2k131Cw1mOrgkGh580UR1qC/ft 9F6xT9GnTNqZUm+LTo3/7japr+CplqWrKxZsfB0+iyp/QhuWA8YOkzHec/5UZOsR+OFQgy jwrI+sl2p83msMxWQ7+l+1jD+f91BFo= ARC-Authentication-Results: i=1; imf21.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=fGXDlnyO; spf=pass (imf21.hostedemail.com: domain of usama.arif@linux.dev designates 91.218.175.180 as permitted sender) smtp.mailfrom=usama.arif@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1786357203; b=L8OZX/GKZCnOH3x7wEIbO8qGGRfMFENRRtGjTC6oIY945oP7XQ7C9UwDfjjilBiH0/X1pq 0qF/CwSBAMGlQ6B7ty6QyzpsTmvkoF6ejUo28qOcgpIIJyZzUQl/oi4li2WTxhAUWHhMJb 7t3c2+RO8tMXqGJFDd8AuoLEJnnaPpw= 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=1786357201; 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: in-reply-to:in-reply-to:references:references; bh=2kxNcoz88gUTv2RyDdUD2oJ4g9y+1zQ1kNSN4EE2fzA=; b=fGXDlnyOZW78tBnMnlQ1tn0gaqx7mSxN8jnpxd3X5ZBs5A+AHB+T0i5Ka2ATUkpwOgnsv1 KMqRp0Augsx1/HsaVXbYVEtsd6TD99UKyuJ+3mT8utVuks9GQoMS+0WK8+l44Y4crMrbtQ xIGnFQ0O2uyU8LD3THLBVtNK7IeoZsw= From: Usama Arif 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 Date: Mon, 10 Aug 2026 03:19:52 -0700 Message-ID: <20260810101954.822260-1-usama.arif@linux.dev> In-Reply-To: <20260715103516.2410175-1-usama.arif@linux.dev> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 8B2C21C0007 X-Stat-Signature: rqo9hqdc51mkrhaea1sdhmot4u7sc7z7 X-HE-Tag: 1786357203-390185 X-HE-Meta: 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 DCKuqR+t 05kG7rHT8QuZz0Si2rx+RwoZfJIwY5R1Qde5okhaRUJF7wsS3lhwGeNugO+KfG20GfXSPl8gCzZD2wTQ3V/ghQYowKcV/zj8mvVd39Fd+uqNafgK+dgiqOpJ4scSITI2LO1bPgoXhxS0OTMYTjjioSDRdP36UkSgBsiqpNsksnKNxcIxYuBF3pF6bqU4DM3eqOpGgzgxsIt7L0mWsG5aLzH3VWcKEKCPLw03IUp4eYxyLZfYR6yJQR1nCfajTFFeeUIZnBAt8EJCh4JUswQV0AnyFEQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 15 Jul 2026 03:35:16 -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) > --- > 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); Hi Christian, It looks like the changes in fs/super.c didnt make it into the patch that was merged in vfs.fixes [1]. Just wanted to check how we could correct this? Should Qi (or I) send a followup patch? Thanks, Usama [1] https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git/commit/?h=vfs.fixes&id=0ef8faff490be6aa1a1e5dfcb0c8492689e91c0f