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 4FCF9FD0048 for ; Sun, 1 Mar 2026 04:10:36 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 07D8D6B0005; Sat, 28 Feb 2026 23:10:35 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 0011F6B0089; Sat, 28 Feb 2026 23:10:34 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id E24AC6B008A; Sat, 28 Feb 2026 23:10:34 -0500 (EST) 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 CEF0A6B0005 for ; Sat, 28 Feb 2026 23:10:34 -0500 (EST) Received: from smtpin17.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 40F4F13B1B0 for ; Sun, 1 Mar 2026 04:10:34 +0000 (UTC) X-FDA: 84496167588.17.EDB49CA Received: from mail-pl1-f169.google.com (mail-pl1-f169.google.com [209.85.214.169]) by imf24.hostedemail.com (Postfix) with ESMTP id 5F914180005 for ; Sun, 1 Mar 2026 04:10:32 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=gmail.com header.s=20230601 header.b=cqIeyuF2; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf24.hostedemail.com: domain of 21cnbao@gmail.com designates 209.85.214.169 as permitted sender) smtp.mailfrom=21cnbao@gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1772338232; 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-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=bfkmYxNazmSUYov2VmIhFLWiffqz1ZOTBMBqaFvFj04=; b=Tz+ctADh1U8qDkPnij6VyPBmlgJC0wFu5DwNvmVBvRb/nhl3Ou9KUm9CUOylLlZfuNjkxx NevFPUc89z0/PgiESXI7ootDU8aHs+/IQ3yG0Z92Lr/ZkcilFGAp+nFs2NOuHBm633Nk8n 7Cd6iKl0N7lxdNeckC1kHfDEdKlTZhs= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=gmail.com header.s=20230601 header.b=cqIeyuF2; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf24.hostedemail.com: domain of 21cnbao@gmail.com designates 209.85.214.169 as permitted sender) smtp.mailfrom=21cnbao@gmail.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1772338232; a=rsa-sha256; cv=none; b=Lb3OkH263/kppWVo9xe+PkpAUYA5W+Q3aWiq/gi2h4wy1kuzWvVdrLVfLGkRSvzxp+Jh65 kPLdQSsAkjS+A0AP+mnG39NFcMSAvCg01EweWjqnhoJzyaflXaM6YyMzNSpIcUH6g2vLQz 5kchsR/YegHqQavKo7oqu3QMAZWV/t0= Received: by mail-pl1-f169.google.com with SMTP id d9443c01a7336-2ae43042ea7so6759905ad.0 for ; Sat, 28 Feb 2026 20:10:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1772338231; x=1772943031; darn=kvack.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=bfkmYxNazmSUYov2VmIhFLWiffqz1ZOTBMBqaFvFj04=; b=cqIeyuF2lvGF90T4SkZ/QK9itiDTWGlYnUr8wvk74/kL0vnBafoytSz3bXtI1+U8tq DcoIiqhX6ElfgxUWeBvAkIk+GR4EG5ulluuMhJJoR122scYP1bJBxdAe2mnXWZgY3MSu r1o/JzOU65oSGX/O3v7nCbZdmEsMWEMWWoE+WK2th3mLYNeR+ZoEpviJknw5bqnBq/E1 iQOtqNuWodjUgcnoRx1TH6S+0UYy/5ekCw1llJDV9/O7DbXa4cCeKJp/ONxLTZfD42vV kWtSCjxa+M+KQkNEyGiejfnhC+89+01WLxJ9AjwSLwjAGoTqGx4dJqhLNUvvPrtCbQVI FGyA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1772338231; x=1772943031; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=bfkmYxNazmSUYov2VmIhFLWiffqz1ZOTBMBqaFvFj04=; b=srW/syvKs3PxPz/Qtmwvc46BdBtqEmw5DRynNtCs1FUf/nnGRXpsTNFLhQoyH63ji2 DsM/mEmMOl4mE6i+YDB6fVLYalADyjvpvcWAFISimAhrbMgjpZMax8KOpBRqEp3T+8Ss lTtg0E1C2UdDI0e88kBcgx7f/PupFSjuIvXBGX5jhC6pig8L0mE2Ua/yXnw7s/e87GZ4 mzdkUPwTHSjumCTdji2genGMZpUQapjoFss8f4/zkJiNve6SXfqVKsURgPvUj/aVjJB7 A/icd9PlygGiDvwc7yCYRr81arRGQE91qnq+/vT+qjDNS1wYKJ00f+fJaO1VtITYxXVg 7pDA== X-Forwarded-Encrypted: i=1; AJvYcCUIg+FGWUZPcaBvkznpuqAF9xnLpHvq2HOjGCKwu9UxQ2oDkRR2skRT5TebiVi70241TOJ0QiU5nw==@kvack.org X-Gm-Message-State: AOJu0YzbiN1A8YlMHL/iwgGSaqhH5UPnKiarVuWsGxLOyCZTwEJdt2mt iua5oAx4AIhKYYrSKmYDqmNIYUZHBlowcukK4Cif3hxx3zMPjnTS2ZwA X-Gm-Gg: ATEYQzw8UWN2uHIFVQ7UZvDMld0x+W8cNoJFOAIddVHyF29bkxZvxSlVCTGPxtO20oj IhwMhmh2Cg9VQUfznJAQPIms8bpwG1Prz7bIQdjrjKzppmHJbuuffb13J4zgZoVcPkmwZDP2rzL gVXSSGW2FeCeZVx3JAyiOAWG0eSXjN84RxOnXw+ddaW+9Cz2eePgOl+By3ulwIxqeZ6PrrfUhD8 XHpFzyFbuJwL19Wr0W1PtKUUZLeyH5rAYCS0KJop5gdaL+pydxeQKVJL2rj1bFdOigxasBXcXK7 JUeVNbIecv1xrBT1O61zmlNOllrtK0SdqgU/ZvLhraXzIEle2vcIK8431eufnBTNsOIm5H4v6L8 Q45Mcq6nWCI7zOxLbuiKYx2JyEe486mBY5AtBON9LwCYRAJzIpx/6AKDU997tnydDQc616dQQ7B owYjbhBQ/kytZjuInx4ow0VMO2flGRSCGd+pHt X-Received: by 2002:a17:903:2c8b:b0:2ae:4a4:f483 with SMTP id d9443c01a7336-2ae2e4bbd3amr79194265ad.49.1772338230844; Sat, 28 Feb 2026 20:10:30 -0800 (PST) Received: from Barrys-MBP.hub ([47.72.129.29]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ae489c3626sm8136105ad.8.2026.02.28.20.10.26 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Sat, 28 Feb 2026 20:10:30 -0800 (PST) From: Barry Song <21cnbao@gmail.com> To: lenohou@gmail.com Cc: 21cnbao@gmail.com, akpm@linux-foundation.org, axelrasmussen@google.com, laoar.shao@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, weixugc@google.com, wjl.linux@gmail.com, yuanchu@google.com, yuzhao@google.com Subject: Re: [PATCH] mm/mglru: fix cgroup OOM during MGLRU state switching Date: Sun, 1 Mar 2026 12:10:22 +0800 Message-Id: <20260301041022.66111-1-21cnbao@gmail.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 5F914180005 X-Stat-Signature: jc4bqndm8wyiw3cygr8ud51craczh4cy X-Rspam-User: X-HE-Tag: 1772338232-991196 X-HE-Meta: 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 vF7nNOEs 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, Mar 1, 2026 at 6:41 AM Barry Song <21cnbao@gmail.com> wrote: > > On Sun, Mar 1, 2026 at 5:28 AM Barry Song <21cnbao@gmail.com> wrote: > [...] > > > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > > index 3e51190a55e4..ba306e986050 100644 > > --- a/include/linux/mmzone.h > > +++ b/include/linux/mmzone.h > > @@ -509,6 +509,8 @@ struct lru_gen_folio { > >         atomic_long_t refaulted[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS]; > >         /* whether the multi-gen LRU is enabled */ > >         bool enabled; > > +       /* whether the multi-gen LRU is switching from/to active/inactive LRU */ > > +       bool switching; > >         /* the memcg generation this lru_gen_folio belongs to */ > >         u8 gen; > >         /* the list segment this lru_gen_folio belongs to */ > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 0fc9373e8251..60fc611067c7 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -5196,6 +5196,7 @@ static void lru_gen_change_state(bool enabled) > >                         VM_WARN_ON_ONCE(!state_is_valid(lruvec)); > > > >                         lruvec->lrugen.enabled = enabled; > > +                       smp_store_release(&lruvec->lrugen.switching, true); > > Sorry, I actually meant: > >  +                       smp_store_release(&lruvec->lrugen.switching, true); >                          lruvec->lrugen.enabled = enabled; > > But I guess we could still hit a race condition in extreme cases—switching > MGLRU on or off as frequently as possible. The only reliable way is to check > enabled during shrinking while holding the lruvec’s lock. Sorry, I was talking to myself.... Since the switching and the 'enabled' state are not inherently serialized with shrink_lruvec(), their values can change at any time, leading to race conditions. Therefore, I believe the only safe approach is: 1. Do not allow enabling or disabling MGLRU on an lruvec while    shrink_lruvec() is running. 2. Do not allow shrink_lruvec() to run while MGLRU is being enabled    or disabled on that lruvec. Something like the following: diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 3e51190a55e4..c4b07159577e 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -509,6 +509,7 @@ struct lru_gen_folio { atomic_long_t refaulted[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS]; /* whether the multi-gen LRU is enabled */ bool enabled; + struct rw_semaphore switch_lock; /* the memcg generation this lru_gen_folio belongs to */ u8 gen; /* the list segment this lru_gen_folio belongs to */ diff --git a/mm/vmscan.c b/mm/vmscan.c index 0fc9373e8251..aadf1e7c31cf 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -5190,6 +5190,7 @@ static void lru_gen_change_state(bool enabled) for_each_node(nid) { struct lruvec *lruvec = get_lruvec(memcg, nid); + down_write(&lruvec->lrugen.switch_lock); spin_lock_irq(&lruvec->lru_lock); VM_WARN_ON_ONCE(!seq_is_valid(lruvec)); @@ -5204,6 +5205,7 @@ static void lru_gen_change_state(bool enabled) } spin_unlock_irq(&lruvec->lru_lock); + up_write(&lruvec->lrugen.switch_lock); } cond_resched(); @@ -5680,6 +5682,7 @@ void lru_gen_init_lruvec(struct lruvec *lruvec) lrugen->max_seq = MIN_NR_GENS + 1; lrugen->enabled = lru_gen_enabled(); + init_rwsem(&lrugen->switch_lock); for (i = 0; i <= MIN_NR_GENS + 1; i++) lrugen->timestamps[i] = jiffies; @@ -5780,10 +5783,14 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) bool proportional_reclaim; struct blk_plug plug; - if (lru_gen_enabled() && !root_reclaim(sc)) { +#ifdef CONFIG_LRU_GEN + down_read(&lruvec->lrugen.switch_lock); + if (lruvec->lrugen.enabled && !root_reclaim(sc)) { lru_gen_shrink_lruvec(lruvec, sc); + up_read(&lruvec->lrugen.switch_lock); return; } +#endif get_scan_count(lruvec, sc, nr); @@ -5885,6 +5892,9 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc) inactive_is_low(lruvec, LRU_INACTIVE_ANON)) shrink_active_list(SWAP_CLUSTER_MAX, lruvec, sc, LRU_ACTIVE_ANON); +#ifdef CONFIG_LRU_GEN + up_read(&lruvec->lrugen.switch_lock); +#endif } /* Use reclaim/compaction for costly allocs or under memory pressure */ -- Thanks Barry