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 7F8D4C44501 for ; Fri, 10 Jul 2026 15:43:57 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 5AEC86B0098; Fri, 10 Jul 2026 11:43:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 55F9F6B0099; Fri, 10 Jul 2026 11:43:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 475B96B009B; Fri, 10 Jul 2026 11:43:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 133546B0098 for ; Fri, 10 Jul 2026 11:43:56 -0400 (EDT) Received: from smtpin01.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 9C0EA1C3945 for ; Fri, 10 Jul 2026 15:43:55 +0000 (UTC) X-FDA: 84973287630.01.EE4065E Received: from out-179.mta0.migadu.com (out-179.mta0.migadu.com [91.218.175.179]) by imf03.hostedemail.com (Postfix) with ESMTP id A0ABC20016 for ; Fri, 10 Jul 2026 15:43:53 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=cDeQqpyd; spf=pass (imf03.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.179 as permitted sender) smtp.mailfrom=qi.zheng@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=1783698234; 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=/60L6Gw7LaN6NkHAg/NT5Zrh/O6NlqQ8F4DkibQxuFk=; b=KuFZkHFOshGkkHwts8LaeVno1I7qVzYBRmLNoirP9p7Gj1njNcVGJrXRMiZ3uPu2R8eOlK rkdIe3HuwAiDX5LdJqkqn6sEIGMSyTrySCRLL0Ir36rqnpNYF5etbw8ZbgdwTu/a9KEkIa JwkYsuk2+L0zxMEofnhPS0GgAdF8ATg= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=cDeQqpyd; spf=pass (imf03.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.179 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=1783698234; b=nkS+JhcUtB8iTofWglac1SX85Si1UErYtkps6m9jvS+FNp60QNR46bxpRvb9OSwkZzv+7c CnqTvzWT9/Ajb5F5byt64Lo4e+cLYLrGeM2hiKsbH22uVG4Sr0iQMZ+2GXWQXS2WjrVk+z ux6U8Qx6Adgivt+KB8P9W69dgwMfApo= 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=1783698231; 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=/60L6Gw7LaN6NkHAg/NT5Zrh/O6NlqQ8F4DkibQxuFk=; b=cDeQqpydjIuRjVm7QrrG8tYD4fmABjnIWojxi26sfQ6ogWR+27YgI1RC1Djgt55UpXsodx R/poROmIofG4314ypP+lOm1nQ5seu5a3JlyBg225TeR2wh8zDKM7xPdbH1GoAvTYtHJLLs CdIxtvMDSyNySfxhJt0G6kp8xJkWv0c= 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 v5] mm: mglru: fix stale batch updates after memcg reparenting Date: Fri, 10 Jul 2026 23:43:18 +0800 Message-ID: <20260710154318.75388-1-qi.zheng@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: A0ABC20016 X-Stat-Signature: 8rjn4mghhcfhrybfkqcex6xrabnj3rk6 X-HE-Tag: 1783698233-722150 X-HE-Meta: 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 ZBVv0cvY tS6z/ithuMd2ATqhyXpOiB/alq1+LzN+yRLuLlN8fI5DckGTlk96lnqSXlUKi1P4Q1Iipj+eUDGcgbGdligsFdD7L6B+aMjPNXMe4ncfS17hGj7+w/lF6DeJvBEoBOVuyJcYWU/kP4OKqolR5uTJIzwzygxtTjYBJgVcp1DzQ7pUr5pl6wVeYIVnX+qC1M9kksWBbfJNMuz5cWUxy21ACIwPgciEFyZHfDXaBbRyEq+J22/j0Y6m3eHfATw== 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 v5: - rename lock_batch_lruvec() to lruvec_live_lock_irq(), and move it to include/linux/memcontrol.h (suggested by Johannes and Shakeel) 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 include/linux/memcontrol.h | 25 +++++++++++++++++++++++++ mm/vmscan.c | 11 ++++------- 2 files changed, 29 insertions(+), 7 deletions(-) diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h index e1f46a0016fcf..9572606776781 100644 --- a/include/linux/memcontrol.h +++ b/include/linux/memcontrol.h @@ -1472,6 +1472,31 @@ static inline void lruvec_lock_irq(struct lruvec *lruvec) spin_lock_irq(&lruvec->lru_lock); } +static inline struct lruvec *lruvec_live_lock_irq(struct lruvec *lruvec) +{ +#ifdef CONFIG_MEMCG + 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); +#else + lruvec_lock_irq(lruvec); +#endif + + return lruvec; +} + static inline void lruvec_unlock(struct lruvec *lruvec) { spin_unlock(&lruvec->lru_lock); diff --git a/mm/vmscan.c b/mm/vmscan.c index 35c3bb15ae96a..1a142c58700d0 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -3265,7 +3265,7 @@ static void update_batch_size(struct lru_gen_mm_walk *walk, struct folio *folio, static void reset_batch_size(struct lru_gen_mm_walk *walk) { int gen, type, zone; - struct lruvec *lruvec = walk->lruvec; + struct lruvec *lruvec = lruvec_live_lock_irq(walk->lruvec); struct lru_gen_folio *lrugen = &lruvec->lrugen; walk->batched = 0; @@ -3285,6 +3285,8 @@ 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 +3781,8 @@ 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 +4866,7 @@ 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