From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-136.mta0.migadu.com [91.218.175.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8A58C423EAE for ; Fri, 11 Sep 2026 08:01:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789113678; cv=none; b=noFBOSmwBwYuR66O+dkVEpACBU5r4tZSVTGA/yDjXlptSfCfPcQUrXxGhnxS5fFTayucAZORL6sB9Ci1608wOHG30Aqf6UrAVE4aOmJsbgihNZaMe9B7XqxemXroWC24Qog024ALNsZcHmAqoZeOnMIeTjZyIyY8zFUZIKFQL9M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789113678; c=relaxed/simple; bh=OKkfFQ/5u1ZQ06ulHO9rwS0KYJDTzNO4EMxRVAB2baU=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=phUv3tGBmFLGDATQlBuXND6dL1Ic836Aw/A9H1B3gOQLg47vcr/ZHDjJB4rqmFOPPip3WPZHqhSY7dVRJ8Xe+3aBxrWEm07N2UKHm9Y7god0FIMYh/thuAuXilw+fCC7v7pc31K7g2p/XEPek/BGUwL8muYs4VLv95HE+LxzUoM= 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=dHNE8/Cn; arc=none smtp.client-ip=91.218.175.136 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="dHNE8/Cn" X-Envelope-To: linux-kernel@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=OKkfFQ/5u1ZQ06ulHO9rwS0KYJDTzNO4EMxRVAB2baU=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1789113672; v=1; x=1789718472; b=dHNE8/Cny96RhIuRk/dZscC6RK6INg30/jQLti7Lei1AJuy3BkbEVjfLE+F5Gw/I2SWdpQhq D4UAFvpHdAy3eIi9Cjq4HkZUL/uR+B38NyhGzoTkzUscVomIsRZUSK7CSdcE5Lp3LY1buxd5D6w SUEORgoSuF2ywt4EskN09jm4= X-Envelope-To: linux-kernel@vger.kernel.org Received: by mta12.migadu.com with ESMTPS id bcd983cb8d37cc8f; Fri, 11 Sep 2026 08:01:12 +0000 X-Mizu-Trace-ID: bcd983cb8d37cc8f X-Migadu-Flow: FLOW_OUT From: Hui Zhu To: Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , David Hildenbrand , Qi Zheng , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Hui Zhu Subject: [PATCH v5 0/4] mm: workingset: fix the shadow node budget under MGLRU Date: Fri, 11 Sep 2026 16:00:47 +0800 Message-ID: X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Hui Zhu Commit 7404bd37cfbe ("mm: workingset: use lruvec_lru_size() to get the number of lru pages") broke the workingset shadow node budget under MGLRU: lruvec_lru_size() reads mz->lru_zone_size, which MGLRU never maintains, so count_shadow_nodes() sees the evictable LRU lists as empty and the shadow shrinker reclaims eviction tokens almost as fast as they are created, losing thrashing protection. Patch 1 extends the dying-mcg stat redirection (previously cgroup v1 only) to all hierarchies, addressing the reparenting race that motivated 7404bd37cfbe. Patch 2 then switches count_shadow_nodes() back to lruvec_page_state_local(), which both classic LRU and MGLRU maintain. Patch 3 recovers the performance. Patch 1 added an unconditional rcu_read_lock() to the stat update fast path; patch 3 checks memcg_is_dying() first and takes the RCU lock only on the rare dying path. Patch 4 closes an accounting gap that patch 2 makes visible: on cgroup v2, reparent_state_local() never moves the dying memcg's non-hierarchical lruvec stats to the parent, so the parent receives the uncharges without the matching charges and its state_local underflows. Patch 4 reparents those stats, mirroring cgroup v1. Performance testing =================== The test script and the raw results are available at [1]. Environment: 10-vCPU QEMU guest, 8 GiB RAM, cgroup v2; 7 runs per configuration, medians reported. Workloads: w1-anon-churn: single-threaded anon fault/charge loop in a memcg (MADV_DONTNEED + re-fault, no reclaim). Every touch is a real fault with charge and memcg stat updates, so it stresses exactly the fast path patch 1 changes. This is the meaningful signal: it is not reclaim-bound, so the small fast-path overhead is not drowned out. w2-file-churn: file read loop under memory.high pressure (reclaim-bound; the differences below are within run-to-run noise and are shown for completeness only). w3-reparent: reparent accounting sanity check. w1-anon-churn (pages/s): classic LRU MGLRU base 4393028 4377122 patches 1-2 4385996 (-0.2%) 4352887 (-0.6%) patches 1-3 4381832 (-0.3%) 4377053 (+0.0%) w2-file-churn (MB/s): classic LRU MGLRU base 8277 8226 patches 1-2 8226 (-0.6%) 8123 (-1.3%) patches 1-3 8157 (-1.4%) 8294 (+0.8%) w3-reparent passed on all kernels. The small overhead visible with patches 1-2 comes from the redirection added by patch 1; patch 3 brings w1 back to the base level in both LRU configurations. The w2-file-churn differences are within run-to-run noise: that workload is reclaim-bound and too noisy to expose the small fast-path overhead, so w1-anon-churn is the meaningful signal. Patch 4 only touches the memcg offline path and is not exercised by these workloads. [1] https://gist.github.com/teawater/32f373ec41d185d840455eb167321a5a Changelog: v5: According to the comments of Andrew, clarify the performance testing section: the w2-file-churn differences are within run-to-run noise; w1-anon-churn is the meaningful signal. v4: According to the comments of Andrew, Fix "follow-up patch" to "preceding patch" in the commit message to match the reordered series. According to the comments of Sashiko, add patch 4 to reparent the non-hierarchical lruvec stats on cgroup v2 to fixing the state_local underflow. v3: According to the comments of Shakeel, reorder the series per review, add Fixes/Cc stable and the user-visible impact to patch 1. Hui Zhu (4): mm: memcg: redirect stats updates of dying memcgs for all hierarchies mm: workingset: use lruvec_page_state_local() to count lru pages mm: memcg: skip the RCU lock when the memcg is not dying mm: memcg: reparent non-hierarchical lruvec stats on cgroup v2 mm/memcontrol-v1.h | 5 ++-- mm/memcontrol.c | 72 +++++++++++++++++++++++++--------------------- mm/workingset.c | 5 ++-- 3 files changed, 45 insertions(+), 37 deletions(-) -- 2.43.0