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 8EBFEC43458 for ; Wed, 1 Jul 2026 07:54:08 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 92F496B00AE; Wed, 1 Jul 2026 03:54:07 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8E0556B00AF; Wed, 1 Jul 2026 03:54:07 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 7D1576B00B0; Wed, 1 Jul 2026 03:54:07 -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 501F96B00AE for ; Wed, 1 Jul 2026 03:54:07 -0400 (EDT) Received: from smtpin20.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id CA39C1A0295 for ; Wed, 1 Jul 2026 07:54:06 +0000 (UTC) X-FDA: 84939444492.20.13000D6 Received: from out-183.mta1.migadu.com (out-183.mta1.migadu.com [95.215.58.183]) by imf30.hostedemail.com (Postfix) with ESMTP id 801B38000A for ; Wed, 1 Jul 2026 07:54:04 +0000 (UTC) Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=gtC108Cj; spf=pass (imf30.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.183 as permitted sender) smtp.mailfrom=qi.zheng@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=1782892445; b=hlTzD2Rtwn41+9gBziYykHUrEU1HjAB3UeCqU1SDfreqXh+MHripzOtb60yyZkfUGGWluk RTPfNHR9tIJV+7xiq3EPraiHUQv1lzXY9HU5dZvaM+Xmz7AqQ1wrrwc6G07HYGbSqoUdYn p7IK6/8l3TadmpWYeJ09Nh7Ww8EGx3o= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1782892445; 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:references:dkim-signature; bh=3h7CGvVoalB/WWwlHPJ/8L12bWTkcsodPzdppqEOSlE=; b=iToHM+h1FwOSH9GzkKGI5aVuau2vUhTZixqPBTuQA3agCnULnyadS18UADUJVC7b1bymBj wTqq7MVRAWMw6kUdm3krEWJ4ZNDO0uUQpQZMvxvPcjK/lvBGp8KpFOuVzKvcgt70NTPaNr ONMhuhXQVGUO47gFxMkvTd6wloztHe0= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=gtC108Cj; spf=pass (imf30.hostedemail.com: domain of qi.zheng@linux.dev designates 95.215.58.183 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev; dmarc=pass (policy=none) header.from=linux.dev 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=1782892442; 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=3h7CGvVoalB/WWwlHPJ/8L12bWTkcsodPzdppqEOSlE=; b=gtC108CjJNVRGfhHG3RKkQAts4kg9aEW1C4fta5PvdlcJFWdsxKhyc5MDoAVC+TJsvhYq9 el42sk6fHOI4mNYDlHkVyL1NPiZXzMgltpKb+XA0Fnr/UfLwbQebwz4eHsSXR9JBV1fNf1 kBHcR2u4vhCRr6IG8Tqm59CGsZDDkQA= From: Qi Zheng To: akpm@linux-foundation.org, david@kernel.org, kasong@tencent.com, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, hannes@cmpxchg.org, harry@kernel.org, muchun.song@linux.dev, peiyang_he@smail.nju.edu.cn, mhocko@kernel.org, roman.gushchin@linux.dev, ljs@kernel.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qi Zheng , stable@vger.kernel.org Subject: [PATCH v4] mm: mglru: fix stale batch updates after memcg reparenting Date: Wed, 1 Jul 2026 15:52:51 +0800 Message-ID: <20260701075251.56413-1-qi.zheng@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: ytzwr4kmk5n7x4pwyrme1zw1iku78ezk X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 801B38000A X-HE-Tag: 1782892444-357803 X-HE-Meta: U2FsdGVkX1/sOck6by0w3Yc/4I9Rd5yKk4s/Fax/dt5qG0jGWR8bRAauwSGTLjBezP/3lD95dqVDog7pXoQve8BDru4sIPLBsoeqOB1xOwRrWRcLuiik9HRS0zWPPVASYlNyqyWMN+d+Cqigj15NP9e2FqcZ6veKN1Rqr+lC51tAaW2A6j95t7T8ZAU0KxTRiXdAU9Zu0ezrULtX+S25kkPZr6Vy5etmSgqbAldfxuI/ctj8CuIS1xaF3TJpoqcG49yIxdWna07pJQorPAGR+1z96Tugx69Ap25j0uaNvc/KGacxC/mSbde90t9pdWlmVTkIhCpra64RzcJbbNIfdXO5I2ruVG2RqSaV3JdcZ52LZwusO1qrBYRmgAHchsW+T/hu4P9OWc5fjEe/bs/Lub33MNwZp3u24jAQqSN/k/pFLKRFDWid4mnRSFZRhZiIgdALA7cWRx9y+Gacey+Tcud4D11q073lX92qzEmVlUhHd5juFnbKRDz5Z3Gjc7Ak4Xozrvlb224dT1tFw+IwCNMMJm6+JqklDbmlZWy9pvA+vcdFM9TohZBe1dVa06VSsW2fguUcoN/5BUC1h6MWVeriFYLCyueirC21HhcjTawrHPGIpGSbBbzhrTZKLsNRyzrGntdO7sJ8TmgDURUWd2KzO9/jxQQYKQs4bxxQzUNBe0I3xezp6q38qqz4lmWwRM3aocTYLe3R81pm6Sr337YfvBoL9YqdYv2UxDTJ5FIcwzXld7xIn5bDAUNFRVU7J5xB20sdnrfjZDrzyoPf5nR1krypr/lp0yU2FI2BPsDTuqdSVZ/mht3xdxCpjTkvusnzdeWb2GxLYVz9ltcsV+CKjHrY99TOb7A1JB8uPvmqzq7Oppg35f5crzBjOEdgZWTSpn7MpMhhqvEK17SsgX4l1STS8N1RfifDw65XMGULpN/TWCyFUNyzgWqEuZ3LZh5NS2U3nkluoVmLsgS H3/vr9oI sjGWhbIplCvFEIN1fPwNXlmEHlhQpkGX+0tcyDh/dN6gelsku4mlWKzQPLXR/J1YqJYIZ5AqHAyIqta0EphjCbDdZb+wqxreaXLZEWaY+PFcJlFNLNNS06T3ureUGHD3VJnL9w7Wn7TcWmr0QJqPRvTPfA2aS/V4FcTsquSuiyajsbBonDvNqy8kqXYKWZHwN++E8JEIMXVckT/h6aNTP7mqJ2JVwKj983jtbZ/6aG8Vbhy626SSDt2mXbw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Qi Zheng The mglru page table walker batches per-generation size deltas in walk->nr_pages while walking page tables without holding the lruvec lock. The reset_batch_size() later folds those deltas into walk->lruvec under the lruvec lock. The page table walker can run concurrently with the memcg reparenting path as follows: CPU0 CPU1 ==== ==== walk_mm --> walk_page_range --> update_batch_size --> walk->nr_pages += delta mem_cgroup_css_offline --> memcg_reparent_objcgs --> lock lruvec lru_gen_reparent_memcg --> reparent child folios to parent unlock lruvec lock lruvec reset_batch_size --> child lrugen->nr_pages += delta This will trigger the following warning in lru_gen_exit_memcg(): VM_WARN_ON_ONCE(memchr_inv(lruvec->lrugen.nr_pages, 0, sizeof(lruvec->lrugen.nr_pages))); And the user-visible impact of underestimated nr_pages in MGLRU was premature OOMs because MGLRU does not try to reclaim memory when nr_pages reaches zero, but there are still more pages. To fix it, make reset_batch_size() check CSS_DYING under RCU before flushing the pending batch. A non-dying memcg keeps the original lruvec stable against RCU-delayed offlining; a dying memcg redirects the deltas to the first non-dying ancestor. Reported-by: Peiyang He Closes: https://lore.kernel.org/all/5A9E929D82717101+12fcf643-efb8-4b9a-a53a-1e28cc894f0b@smail.nju.edu.cn Fixes: f304652609ea ("mm: vmscan: prepare for reparenting MGLRU folios") Cc: Signed-off-by: Qi Zheng Reviewed-by: Harry Yoo (Oracle) --- Changes in v4: - re-implement lock_batch_lruvec() in a simpler way (suggested by Johannes and Harry) - collect Reviewed-by - rebase onto the next-20260630 Changes in v3: - re-implement lock_batch_lruvec() by checking CSS_DYING under the RCU lock (suggested by Harry) - update the commit message (suggested by Harry) - temporarily drop the previous Reviewed-by tags (since the sync method has changed) - rebase onto the next-20260624 Changes in v2: - update the commit message (pointed by Barry) - collect Reviewed-by mm/vmscan.c | 41 ++++++++++++++++++++++++++++++++++------- 1 file changed, 34 insertions(+), 7 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 35c3bb15ae96..ca1e2a870d51 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3262,10 +3262,40 @@ static void update_batch_size(struct lru_gen_mm_walk *walk, struct folio *folio, walk->nr_pages[new_gen][type][zone] += delta; } +#ifdef CONFIG_MEMCG +static struct lruvec *lock_batch_lruvec(struct lruvec *lruvec) +{ + struct pglist_data *pgdat = lruvec_pgdat(lruvec); + struct mem_cgroup *memcg = lruvec_memcg(lruvec); + + rcu_read_lock(); + + /* + * The memcg can be NULL when the memory controller is disabled. + * Otherwise, the caller keeps the memcg owning @lruvec alive. + */ + while (unlikely(memcg && css_is_dying(&memcg->css))) { + memcg = parent_mem_cgroup(memcg); + lruvec = mem_cgroup_lruvec(memcg, pgdat); + } + + spin_lock_irq(&lruvec->lru_lock); + + return lruvec; +} +#else +static struct lruvec *lock_batch_lruvec(struct lruvec *lruvec) +{ + lruvec_lock_irq(lruvec); + + return lruvec; +} +#endif + static void reset_batch_size(struct lru_gen_mm_walk *walk) { int gen, type, zone; - struct lruvec *lruvec = walk->lruvec; + struct lruvec *lruvec = lock_batch_lruvec(walk->lruvec); struct lru_gen_folio *lrugen = &lruvec->lrugen; walk->batched = 0; @@ -3285,6 +3315,8 @@ static void reset_batch_size(struct lru_gen_mm_walk *walk) lru += LRU_ACTIVE; __update_lru_size(lruvec, lru, zone, delta); } + + lruvec_unlock_irq(lruvec); } static int should_skip_vma(unsigned long start, unsigned long end, struct mm_walk *args) @@ -3779,11 +3811,8 @@ static void walk_mm(struct mm_struct *mm, struct lru_gen_mm_walk *walk) mmap_read_unlock(mm); } - if (walk->batched) { - lruvec_lock_irq(lruvec); + if (walk->batched) reset_batch_size(walk); - lruvec_unlock_irq(lruvec); - } cond_resched(); } while (err == -EAGAIN); @@ -4867,9 +4896,7 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec, walk = current->reclaim_state->mm_walk; if (walk && walk->batched) { walk->lruvec = lruvec; - lruvec_lock_irq(lruvec); reset_batch_size(walk); - lruvec_unlock_irq(lruvec); } mod_lruvec_state(lruvec, PGDEMOTE_KSWAPD + reclaimer_offset(sc), -- 2.54.0