From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-41.mta1.migadu.com [95.215.58.41]) (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 D9E3D1AF0BB for ; Sun, 23 Aug 2026 11:23:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.41 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787484223; cv=none; b=rB5xVdw5PKUyBkbPWpHcw3KPdkcOAkkGAvAjO5ksRZYMPRI3W1mRFlA4ICyZXH1vUMt1kIZqJrHsO/HMtH0waiZKl3HtefxWn5JDDrx5WTbqNWp5CIfRfVGtKFrP97ulmJvbglTVEF/AcUWDZMq7p+qY8SUZ1YtywvgRUzV3kBM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787484223; c=relaxed/simple; bh=scLwNcRfqDAYy7qLpBOIX92qClywJPM/JluY6oTsaJs=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=l9qo/PqN+OvieT+HPw0fg61zJs3/6W1w36TDkgmnS/Ptwz4E7JNdQb5ebvy2401ZVGPHT2fwu3Tw1MO3Jn6UeNDVKi+zd5oOvk5XdbUdcBc4MlWRNxlzBmpEf52S/pEPD2aurb8R3Pv8baEGCeMQwCMNwX1KniHtxrXqRs84G90= 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=uHeGWw+L; arc=none smtp.client-ip=95.215.58.41 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="uHeGWw+L" X-Envelope-To: stable@vger.kernel.org DKIM-Signature: a=rsa-sha256; bh=scLwNcRfqDAYy7qLpBOIX92qClywJPM/JluY6oTsaJs=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1787484217; v=1; x=1788089017; b=uHeGWw+LBLoa72GttgOG7Qd6OJoH4LFjO4o/uU3eXr/wHEeT0OrtM6AAAE0yWuDwdnjtNBTy G4W3ukOEpyomVeGgLd+1VJGt8TAcpMKrKVdHL0dRPxIKHJInGaGh0DhRomv3iwzSNE+rxBULYk9 NnQNvc/RmPMeY5Iq3llgKPtM= X-Envelope-To: stable@vger.kernel.org Received: from DESKTOP-QUF7BT0.localdomain (223.74.103.101) by smtp.migadu.com with ESMTPS id a53add02a007d151; Sun, 23 Aug 2026 11:23:27 +0000 X-Mizu-Trace-ID: a53add02a007d151 X-Migadu-Flow: FLOW_OUT From: Ridong Chen To: Cc: ridong.chen@linux.dev, Ridong Chen , stable@vger.kernel.org Subject: [PATCH] mm/mglru: fix ineffective memory protection for non-kswapd reclaim Date: Sun, 23 Aug 2026 19:22:52 +0800 Message-ID: <20260823112313.189468-1-ridong.chen@linux.dev> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Ridong Chen memory.min/low is silently bypassed for MGLRU during global proactive reclaim (writing to the root memory.reclaim) and global direct reclaim. It can be reproduced as follows: # echo 7 > /sys/kernel/mm/lru_gen/enabled # cd /sys/fs/cgroup # mkdir -p a/b # echo 100M > a/memory.min # echo +memory > a/cgroup.subtree_control # echo 100M > a/b/memory.min # echo $$ > a/b/cgroup.procs # dd if=/dev/zero of=/tmp/testfile bs=1M count=200 # cat a/b/memory.current 222650368 # echo 500M > memory.reclaim -bash: echo: write error: Resource temporarily unavailable # cat a/b/memory.current 6070272 memory.min is 100M, yet reclaim drops a/b down to 6M, breaking the protection. The traditional LRU path is not affected because shrink_node() calls mem_cgroup_calculate_protection() for each memcg it visits during a top-down tree walk. Commit 30d77b7eef01 ("mm/mglru: fix ineffective protection calculation") moved the protection computation into lru_gen_age_node(), which only runs for kswapd. Non-kswapd global reclaim reaches shrink_one() through lru_gen_shrink_node() -> shrink_many() without any protection computation, so emin/elow remain stale or zero. Introduce mem_cgroup_protection_path() which computes emin/elow along the root-to-target path only by iterating through the cgroup ancestors array top-down. This avoids the full tree traversal that would be needed with mem_cgroup_calculate_protection(), limiting the cost to O(depth) per memcg - typically 3-5 levels. Call it from shrink_one() for the non-kswapd path so that each memcg about to be shrunk has correct protection values. Fixes: e4dde56cd208 ("mm: multi-gen LRU: per-node lru_gen_folio lists") Cc: stable@vger.kernel.org Signed-off-by: Ridong Chen --- include/linux/memcontrol.h | 7 +++++++ mm/memcontrol.c | 42 ++++++++++++++++++++++++++++++++++++++ mm/vmscan.c | 3 +++ 3 files changed, 52 insertions(+) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index 8170bb8066a2..4e0dd5d98f3a 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -600,6 +600,8 @@ static inline void mem_cgroup_protection(struct mem_cgroup *root, void mem_cgroup_calculate_protection(struct mem_cgroup *root, struct mem_cgroup *memcg); +void mem_cgroup_protection_path(struct mem_cgroup *root, + struct mem_cgroup *memcg); static inline bool mem_cgroup_unprotected(struct mem_cgroup *target, struct mem_cgroup *memcg) @@ -1126,6 +1128,11 @@ static inline void mem_cgroup_calculate_protection(struct mem_cgroup *root, { } +static inline void mem_cgroup_protection_path(struct mem_cgroup *root, + struct mem_cgroup *memcg) +{ +} + static inline bool mem_cgroup_unprotected(struct mem_cgroup *target, struct mem_cgroup *memcg) { diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 69b37f63a307..e915176ac06b 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -5134,6 +5134,48 @@ void mem_cgroup_calculate_protection(struct mem_cgroup *root, page_counter_calculate_protection(&root->memory, &memcg->memory, recursive_protection); } +/** + * mem_cgroup_protection_path - compute protection along root->memcg path + * @root: the top ancestor of the sub-tree being checked (NULL for root_mem_cgroup) + * @memcg: the target memory cgroup + * + * Walk the ancestor path from @root down to @memcg and compute the effective + * protection at each level. This is safe for isolated queries because it + * ensures parents are computed before children. + */ +void mem_cgroup_protection_path(struct mem_cgroup *root, + struct mem_cgroup *memcg) +{ + bool recursive_protection = + cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_RECURSIVE_PROT; + struct cgroup *cg; + int root_level, i; + + if (mem_cgroup_disabled()) + return; + + if (!root) + root = root_mem_cgroup; + + if (memcg == root) + return; + + root_level = root->css.cgroup->level; + cg = memcg->css.cgroup; + + rcu_read_lock(); + for (i = root_level + 1; i <= cg->level; i++) { + struct mem_cgroup *cur; + + cur = mem_cgroup_from_css(cgroup_css(cg->ancestors[i], + &memory_cgrp_subsys)); + if (cur) + page_counter_calculate_protection(&root->memory, + &cur->memory, recursive_protection); + } + rcu_read_unlock(); +} + static int charge_memcg(struct folio *folio, struct mem_cgroup *memcg, gfp_t gfp) { diff --git a/mm/vmscan.c b/mm/vmscan.c index 4ca9775ceee8..70e28d583255 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -5031,6 +5031,9 @@ static int shrink_one(struct lruvec *lruvec, struct scan_control *sc) struct pglist_data *pgdat = lruvec_pgdat(lruvec); /* lru_gen_age_node() called mem_cgroup_calculate_protection() */ + if (!current_is_kswapd()) + mem_cgroup_protection_path(NULL, memcg); + if (mem_cgroup_below_min(NULL, memcg)) return MEMCG_LRU_YOUNG; -- 2.43.0