From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 94B7D3E5EE7 for ; Thu, 17 Sep 2026 05:11:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789621872; cv=none; b=KRSWmIod23dixqRs0382Mj3hsAGD75w2b91g55VH9myqDxBJ/HnGR5aQuRU0VP59JT790MmMYd3agkqpIFaNLORkoh0WVN0tFvCWNySfRVWjCSL+vvR1hwEI5xNpFhrjK0G4XWDIx4ySI9jWu13scPJjWmPE6kqG6XRQl3IEF+s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789621872; c=relaxed/simple; bh=WTHxLW7BS1jTaYa80VF2QCxeGIyI5UQMX/d0iagKAc8=; h=Date:To:From:Subject:Message-Id; b=fRsphT4VW/t/awe25leFn/nrAuDnr9FRdquVb+1nLVkDB3JRcQuyfbHKAgyVhSHPUgXXR1Mbk37eytrScAD4PRNkQDkpWMJxFxbFV7KQxvBpYbbua5RKgJb//3WSQtBxvawnJB2sJSYGFj5UiZmhaoVVwadNdRBTV8NqVHsooTU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=gXs+fKk1; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="gXs+fKk1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 28C981F000FF; Thu, 17 Sep 2026 05:11:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1789621871; bh=DJT7RZW40gpK2zD4iZ5H7zQnGhd52O2FAG6pmWuQgDs=; h=Date:To:From:Subject; b=gXs+fKk1ijncL5fv81ZD1zSXGig8L2EH+bNR69QxuXbVoZH9eTdREycmRnBHir9Kx V8GkAc+LXcxwATlV/KX5KI0vIxVi3ZLH3LX2GITtffc9Lb32h7deinzbV0ZBothlvE rRNoerxoUmw/D7YKj5Eapt5UTsg0K4/PvBmDAQQc= Date: Wed, 16 Sep 2026 22:11:10 -0700 To: mm-commits@vger.kernel.org,zhuhui@kylinos.cn,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-memcg-skip-the-rcu-lock-when-the-memcg-is-not-dying.patch added to mm-unstable branch Message-Id: <20260917051111.28C981F000FF@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm: memcg: skip the RCU lock when the memcg is not dying has been added to the -mm mm-unstable branch. Its filename is mm-memcg-skip-the-rcu-lock-when-the-memcg-is-not-dying.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-memcg-skip-the-rcu-lock-when-the-memcg-is-not-dying.patch This patch will later appear in the mm-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Hui Zhu Subject: mm: memcg: skip the RCU lock when the memcg is not dying Date: Fri, 11 Sep 2026 16:00:50 +0800 get_non_dying_memcg_start() takes rcu_read_lock() on every stat update, but the lock only protects the upward walk to a non-dying ancestor, which happens solely while a memcg is being offlined. The dying check itself reads the CSS_DYING flag of a memcg the caller already holds a reference to, so it is safe without the lock. Check memcg_is_dying() first and return immediately when the memcg is alive, taking the RCU lock only on the rare dying path. On an anon fault/charge churn workload in a memcg this recovers the ~0.6% overhead added by the previous patch (4368077 vs 4343159 pages/s before, back to ~4377000 pages/s after). Link: https://lore.kernel.org/9ffdbdfc96312e3e13cb8f056bfe26649492d949.1789096175.git.zhuhui@kylinos.cn Fixes: 7404bd37cfbe ("mm: workingset: use lruvec_lru_size() to get the number of lru pages") Signed-off-by: Hui Zhu Signed-off-by: Andrew Morton Acked-by: Shakeel Butt Cc: Axel Rasmussen Cc: Barry Song Cc: David Hildenbrand Cc: Johannes Weiner Cc: Kairui Song Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Muchun Song Cc: Roman Gushchin Cc: Wei Xu Cc: Yuanchu Xie Cc: --- mm/memcontrol.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) --- a/mm/memcontrol.c~mm-memcg-skip-the-rcu-lock-when-the-memcg-is-not-dying +++ a/mm/memcontrol.c @@ -881,6 +881,17 @@ static long memcg_state_val_in_pages(int static inline struct mem_cgroup * get_non_dying_memcg_start(struct mem_cgroup *memcg, bool *rcu_locked) { + /* + * Fast path: the caller holds a reference to @memcg, so reading + * its CSS_DYING flag without the RCU lock is safe. The RCU lock + * is only needed to walk up to a non-dying ancestor, which + * happens only while a memcg is actually being offlined. + */ + if (!memcg_is_dying(memcg)) { + *rcu_locked = false; + return memcg; + } + rcu_read_lock(); *rcu_locked = true; @@ -892,6 +903,9 @@ get_non_dying_memcg_start(struct mem_cgr static inline void get_non_dying_memcg_end(bool rcu_locked) { + if (!rcu_locked) + return; + rcu_read_unlock(); } _ Patches currently in -mm which might be from zhuhui@kylinos.cn are mm-vmstat-annotate-data-race-for-per-cpu-pageset-fields.patch mm-memcg-redirect-stats-updates-of-dying-memcgs-for-all-hierarchies.patch mm-workingset-use-lruvec_page_state_local-to-count-lru-pages.patch mm-memcg-skip-the-rcu-lock-when-the-memcg-is-not-dying.patch mm-memcg-reparent-non-hierarchical-lruvec-stats-on-cgroup-v2.patch