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=1794686914; b=SGLDPmfe6Cl8AdC2dmdvoSKjip2sELOlcXYyo3AQmHT1zmCWIjjCMwgSlIegbL5X/dXd j4GcgK/chwAsIOyAn+EPyEPaeDTCTiViF12yMmiA9lB9gAsd2A5qt85dz3GHrqQb+D76I PTU73JVNL2wICXocfj/5nfepvqUPbbuGhm3Scyw15fccN/g9qCXpikwLte7xfIN7pkyiB atlqv4Hn+YH9iThkJ42ScCYy6fqxBQv+uiBiOpprV8gsVWcWXEaSEipIPU2acCWiwUdH9 1irKeHP68p2Tl0/4pY6HI7KNoUUphpx3t3DZfIAaj3R2GQMVisbM3c/4sr4BafyLhyA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794686914; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-Id:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=wpMLEsj5uFCoVB+BC2qF5SnzrdWcHRIuEONv7+JryW0=; b=MdfajE/5jwAAmcJbabFe9E8FL4UGCtdLqojGHMgDymZwEkr+sYU/wK2itkvUgBWtQKJk hIwmaj6rla9Nl1e/lbl09qOugS68A51Gp1UMAK0v50VeRli4b0lHGuVxz02I2KDT5d5SV FB2PMLoy+f+wM4H87TJeDyzRJo1G+PFKZ2fajX6gjSM1sYwUNBXLAlioo35kEnHP3XAmo ZQVzaUvONQDGR+SzECbZ3FT3icdsal0RF9WMfRMvg2sa9FWCsyJBtbNGwChCyAS7mAM8f h3sjOX8gJoGIbszfIz03NwIqzO4+HaQlmAjKTC8oGlsIsluSrPuc9KuD7vCQhfj+Kxg== 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=OCtqX8y5; 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 15106606A330 for ; Sat, 14 Nov 2026 20:08:33 +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=OCtqX8y5 Received: by smtp.kernel.org (Postfix) with ESMTPSA id E85161F000C4; Sat, 14 Nov 2026 20:08:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794686913; bh=wpMLEsj5uFCoVB+BC2qF5SnzrdWcHRIuEONv7+JryW0=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=OCtqX8y5B44sZ6C9lsM9Zu6SFjAstNGCMH9e0WX4luzWLYo5UWAZZAqhdI8WQNgxD 5Ka5txDe8FlB+zIG9KfZD6nOXg9m0Tb/Fx1jvkH2QqzBLrhnO1dK4gKUMXB9VhzHDt BXPReux9t+KhpVkikOKpOpfZVdEr8Y7Bo2H3S6IevpeNo1hucetdc5xeY8ZDsVqMfv J02am1X1WIxO50pPPinD67VNmVj5niabK2dvL3RWeCg0jMH33CafQpjjSdZPtMJqFz f85v+30UEVcClGEhSQf8v5COyzUkYB/RLcTPFLkNm+WwpRR8eMLyRNPR/boojAk1nK cp6vwID0Pwzug== From: "Barry Song (Xiaomi)" To: akpm@linux-foundation.org, linux-mm@kvack.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, 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 v9 04/16] mm/mglru: lift the forced protection of reclaimer Date: Sun, 15 Nov 2026 04:07:51 +0800 Message-Id: <20261114200803.23129-5-baohua@kernel.org> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20261114200803.23129-1-baohua@kernel.org> References: <20261114200803.23129-1-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 thrash more under heavy memory pressure. This should instead be addressed through refault-distance and frequency-aware promotion [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 1197e15065fe..603fb7c73f94 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4677,7 +4677,7 @@ 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); @@ -4694,12 +4694,22 @@ 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); @@ -4754,15 +4764,16 @@ 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)); @@ -4775,18 +4786,24 @@ 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); @@ -4797,8 +4814,7 @@ 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); -- 2.39.3 (Apple Git-146)