From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794439593; b=p+6T5XBkowrglYCeIserStfbd8xykCh9OkqVzQKjyrHT7jrjDW9YLLwo853apMMQY3IN T7wJHW8tEIwrHg5eDJsZ93/ntCYVRpi2CkOZX7qutcv2YXXRGtD76QgY7u0V7NVT+kufW Tw1DRmFFr/biqGfuwAfR5YowlE9b0UXYsOUJTYSHByfuH/8BLCxLByPhMf/cQbsK8ncNi nVGQV4JYQbSrS/0ORyST1NUl/N/lgXq13CmEGgWZpzvAF3mhNKVs8eChblDHoPTGEaVOi ebWfxh87c8JS4IGZqc/wsg+ZkkLaTE6b8kn/zalzX0Jjv2tFBRTfysGUFjr059JNtDg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794439593; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-Id:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=DuTthrTZtfu6mc4h+uORvcmjei37v2/cFoPsDNmHnVU=; b=e4oL0xE/Ktkwa7H3MMH6hWOuCHZ1ZSIZ7N6+TS5wsTZqQVzWQ9Ge/MDLkshhqufdYDzi i0vTERq7/3d4Gp499RzWlk6zXGaE39cKGcbuFlY3sjUM1ctHFn8/g8O42cs/7SDu5okGg Fx7CDiTz/bV4klul+KCxRyxQKIQYlGSRNlSac2AAWbZ0lAZcoW+jNv4qELd2kIjdq1SlA F14RMtOJn1vJWuA2VUTunEDZGFstSubnC3XxBQUCvXnXPIj9vY4tbs+Epibqvu0Tp3Vr5 xPR8fDZp7DUYoYAC+fGuDUBxc7cY0S4ZLIOM1wP6FXk7spOV58QNvugjxkZRqlR2zEw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=PMCDVctK; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 32D33606A32E for ; Wed, 11 Nov 2026 23:26:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=PMCDVctK Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2885D1F00A05; Wed, 11 Nov 2026 23:26:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794439592; bh=DuTthrTZtfu6mc4h+uORvcmjei37v2/cFoPsDNmHnVU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=PMCDVctKY3XCbpJ3J/X8Me0MqNgWypCG09I+v5gX6qCzvPKl9mgOvu+TMq2r6hcki Lic53vw5OTkpwMZKJv19FCd6f6EoUBqAi8xcVeodrInm0UcMPtRrkagSfgr1QrBpuv 7fNihccUamqND1UXG0+ldLBrRs6D5n8SNfwfH4vLl0Tc2H0xkaH8Jop5UI24SuNCuF ap2KbDjW39PgaNnMccGX+UPhFtJnepP5kyLe4WC/jWYd7ztoL/3L34L/K/iMhEpTYu mAe/+i32ivY7wsIv0QI+Di70XnFCdC1Wx3VeVrLI2wLvGdw41YVd4YGCP7kGDIKvR+ 4F5avq2KZkEzQ== From: "Barry Song (Xiaomi)" To: akpm@linux-foundation.org Cc: axelrasmussen@google.com, baolin.wang@linux.alibaba.com, baoquan.he@linux.dev, hannes@cmpxchg.org, hui.zhu@linux.dev, kasong@tencent.com, kunwu.chan@gmail.com, liam@infradead.org, lianux.mm@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, liuxiang.277@bytedance.com, lyugaofei@xiaomi.com, mhocko@kernel.org, mhocko@suse.com, qi.zheng@linux.dev, ridong.chen@linux.dev, rppt@kernel.org, ryncsn@gmail.com, shakeel.butt@linux.dev, surenb@google.com, wangzicheng@honor.com, weixugc@google.com, yuanchu@google.com, zhangbo56@xiaomi.com, zhuhui@kylinos.cn, sidchintamaneni@gmail.com, Barry Song Subject: [PATCH v7 04/16] mm/mglru: lift the forced protection of reclaimer Date: Thu, 12 Nov 2026 07:25:51 +0800 Message-Id: <20261111232603.9934-5-baohua@kernel.org> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20261111232603.9934-1-baohua@kernel.org> References: <20261111232603.9934-1-baohua@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Kairui Song When a type is drained down to MIN_NR_GENS gens, the reclaimer will fail to make any progress on that type without aging. However aging comes with a cost, and it will take time to finish. Even if we do aging more proactively, when under great pressure, gens will still be drained very fast so the new gens produced by aging can't catch up with the consumption. With MIN_NR_GENS setting blocking the reclaim, we will run into OOM. This OOM can be reproduced by the previous test program [1] used for fixing another aging problem [2]. When running in great pressure, certain workloads will keep seeing premature OOM with MGLRU, and never see any OOM with classical LRU. This might get worse if we implement async aging, or avoid hotness inversion in aging, as they will slow down the aging process even more. To fix this, let's first drop the get_nr_gens() == MIN_NR_GENS early return and let the raised-priority scan bound cover max_seq itself. Mapped folios will still survive as the rmap PTE check will keep them. Unmapped cache folios may thrashing more when under great pressure, which is really a problem that should be fixed with refault distance and frequecy aware promotoin instead [3]. Link: https://github.com/ryncsn/emm-test-project/tree/master/file-anon-mix-pressure [1] Link: https://lore.kernel.org/linux-mm/20260428-mglru-reclaim-v7-0-02fabb92dc43@tencent.com/ [2] Link: https://lore.kernel.org/linux-mm/20260502-mglru-fg-v1-0-913619b014d9@tencent.com/ [3] Signed-off-by: Kairui Song Signed-off-by: Barry Song (Xiaomi) Reviewed-by: Kunwu Chan --- mm/vmscan.c | 34 +++++++++++++++++++++++++--------- 1 file changed, 25 insertions(+), 9 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 593f407c0668..db0a8a3e8887 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4672,7 +4672,7 @@ void lru_gen_reparent_memcg(struct mem_cgroup *memcg, struct mem_cgroup *parent, ******************************************************************************/ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_control *sc, - int min_gen, int tier_idx) + int min_gen, int max_gen, int tier_idx) { int gen = folio_lru_gen(folio); int type = folio_is_file_lru(folio); @@ -4689,12 +4689,22 @@ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_c if (!folio_evictable(folio)) return false; - /* promoted */ + /* promoted, or moved due to reparenting. */ if (gen != min_gen) { list_move(&folio->lru, &lrugen->folios[gen][type][zone]); return true; } + /* + * We are reclaiming the last gen left. Folios in this gen can no + * longer be promoted or protected, so just isolate them. The one + * exception is lru_gen_reparent_memcg(), which is handled above. + */ + if (min_gen == max_gen) { + VM_WARN_ON_ONCE(zone > sc->reclaim_idx); + return false; + } + /* protected */ if (tier > tier_idx || refs + workingset == BIT(LRU_REFS_WIDTH) + 1) { gen = folio_inc_gen(lruvec, folio, min_gen); @@ -4749,15 +4759,16 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec, struct list_head *list, int *isolatedp) { int i; - int gen; enum node_stat_item item; int sorted = 0; int scanned = 0; int isolated = 0; int skipped = 0; + int gen, max_gen; unsigned long min_seq; unsigned long remaining = nr_to_scan; struct lru_gen_folio *lrugen = &lruvec->lrugen; + DEFINE_MAX_SEQ(lruvec); VM_WARN_ON_ONCE(nr_to_scan > MAX_LRU_BATCH); VM_WARN_ON_ONCE(!list_empty(list)); @@ -4770,18 +4781,24 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec, if (sc->priority == DEF_PRIORITY) min_seq = lrugen->min_seq[type]; else - min_seq = lruvec_populated_min_seq(lruvec, type, lrugen->max_seq - MIN_NR_GENS + 1); - - if (get_nr_gens(lruvec, type) == MIN_NR_GENS) - return 0; + min_seq = lruvec_populated_min_seq(lruvec, type, lrugen->max_seq); gen = lru_gen_from_seq(min_seq); + max_gen = lru_gen_from_seq(max_seq); + for (i = MAX_NR_ZONES; i > 0; i--) { LIST_HEAD(moved); int skipped_zone = 0; int zone = (sc->reclaim_idx + i) % MAX_NR_ZONES; struct list_head *head = &lrugen->folios[gen][type][zone]; + /* + * If there is only one gen left, rotating the unreclaimable + * zone become meaningless, just skip them. + */ + if (gen == max_gen && zone > sc->reclaim_idx) + continue; + while (!list_empty(head)) { struct folio *folio = lru_to_folio(head); int delta = folio_nr_pages(folio); @@ -4792,8 +4809,7 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec, VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio); scanned += delta; - - if (sort_folio(lruvec, folio, sc, gen, tier)) + if (sort_folio(lruvec, folio, sc, gen, max_gen, tier)) sorted += delta; else if (isolate_folio(lruvec, folio, sc)) { list_add(&folio->lru, list); -- 2.34.1