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=1792706580; b=hkNk/UrXcmvfPAXJ90I9UbcnprbtaSsREo/D+B+qFJEgrK9210eyVdFVwHYpz7Xu5Usz X0hUUmHTW2hBIakVW6+IIIO89GxbDuXoR9DNu5RQ86Ks/6GMU7i9GBxNYDmRwYhpwm2qX 07tTk6iH/vR6DgQyaOwoPPsLONL+nr5UrifMK0zRtO+gNLnUrjKfL4o937NrTjjiMtZRQ 5OotuJFJ+Jba0dlmBgBTD4EXxOt5/Fs8JcFBoMMiePJy/XiVFYXDwG9zf0abVvmX1WV8u 6S+U9KSpG8qSGxB5C1sh1KOb0vOTf8l/OLywBEh0+uiLuoflTxufgPjHDwpWh/FZ6pg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792706580; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-Id:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=9Fk/aE6plvRET0JhkIxplBx62u989q4tddIWIjnOMgs=; b=a/0bna0B86JygyQchv3WwTYM8UKR5SteclpAYwYWENlfZN2rfba+GL7OTJdJTVYZr+Fy U8vmSSmsv3bz5VpSK01EvwcTP395G2b6MFhgqjY2wk5fRHg0do5+T5yLdt7m04r9HWGwR DD8IDktBFieDieLLGc2EoGu2Y2aX8f9gLTnVnHygX64yXcrvHVEkbr/AM5ZypyFAI4I9+ DNttPpObuRRKT9OCt03eTFLxCOr+MG1W1CLTSBdhVnkakHrnOMqRXI5mrS4wHM6dprhid mzbsgQkKZh9Cs+TjIO0hN7nC1iKhcQp8G5pixcbPbVkImO6bktmvQFxoTjvF1ryfYVQ== 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=WOIX0dy5; 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 6617A606A31A for ; Thu, 22 Oct 2026 22:03:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=WOIX0dy5 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1E2C41F031E1; Thu, 22 Oct 2026 22:02:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792706580; bh=9Fk/aE6plvRET0JhkIxplBx62u989q4tddIWIjnOMgs=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=WOIX0dy5cgSndPOgPAQldjDETk22JiUXdVEyYGbp0iSHkphd/STXXnE3qX89ZhYnB rD181A2IsqDtFIFqNfPJw+a63APGdsvgH8mGh8WTrYR1EpbV33/FeUpSwFTfZkq31y ItKEXBT5tUpTRWWhbv7xmdvLTFyIZE/ND5MJga8+9Kh1FyNyEtLfD1WAPBW73to2Xm Hu9reh1OAUtlwxCTTK6Tc7cu88/x2ywxWKbAgd++LSx7pwrhOSgykTAx+KkUGjvIcv UFaACPJpNdtxHNvZr1GMkjr6jGDALaczIKPFXyVPJ8KBkubEXZFkAURaT1OrRii8y9 SwJ1hmQSAZeAA== From: "Barry Song (Xiaomi)" To: akpm@linux-foundation.org, linux-mm@kvack.org Cc: hui.zhu@linux.dev, axelrasmussen@google.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, david@kernel.org, hannes@cmpxchg.org, linux-kernel@vger.kernel.org, ljs@kernel.org, mhocko@kernel.org, qi.zheng@linux.dev, ryncsn@gmail.com, shakeel.butt@linux.dev, weixugc@google.com, yuanchu@google.com, zhuhui@kylinos.cn, baoquan.he@linux.dev, liuxiang.277@bytedance.com, wangzicheng@honor.com, lianux.mm@gmail.com, kasong@tencent.com, liam@infradead.org, surenb@google.com, mhocko@suse.com, rppt@kernel.org, zhangbo56@xiaomi.com, lyugaofei@xiaomi.com, ridong.chen@linux.dev, kunwu.chan@gmail.com Subject: [RFC PATCH v5 09/14] mm/mglru: Avoid placing rejected folios below populated gen Date: Fri, 23 Oct 2026 06:01:58 +0800 Message-Id: <20261022220203.91911-10-baohua@kernel.org> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20261022220203.91911-1-baohua@kernel.org> References: <20261022220203.91911-1-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 We used to scan only the oldest generation in scan_folios(). In evict_folios(), we checked whether lru_gen_folio_seq(lruvec, folio, false) == min_seq[type]. If so, the folio was marked active and moved to younger generations. This was itself buggy, as folios in generation min_seq[type] - 1 would not be marked active by folio_set_active(), potentially causing a cold/hot inversion. Besides this issue, the old approach also differs from the current behavior, where we can scan fewer than two generations. Now that we can scan younger generations, including the youngest generation, this no longer prevents rejected folios from being placed in a generation below or at the populated generation. Such rejected folios would then be scanned again and again, resulting in extremely low `pg_steal/pg_scan` ratios. For example: pgsteal_file: 2312605 pgscan_file: 36465693 reclamation efficiency: 6.34% We pass `scanned_seq` to `move_folios_to_lru()` and make sure we either promote the folio or place it in the youngest generation when the populated generation is already the youngest one. Also, folio_set_active() is no longer needed. With this change, the results become: pgsteal_file: 2683815 pgscan_file: 4224244 reclamation efficiency: 63.53% The sys time for building the kernel also decreased from 4m30.532s to 3m50.188s while swappiness==1. Signed-off-by: Barry Song (Xiaomi) --- include/linux/mm_inline.h | 22 +++++++++++++++++++++- mm/vmscan.c | 24 ++++++++++++------------ 2 files changed, 33 insertions(+), 13 deletions(-) diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h index ab69b9930893..f6f4bc9a704f 100644 --- a/include/linux/mm_inline.h +++ b/include/linux/mm_inline.h @@ -332,7 +332,8 @@ static inline unsigned long lru_gen_folio_seq(const struct lruvec *lruvec, return max(READ_ONCE(lrugen->max_seq) - gen + 1, READ_ONCE(lrugen->min_seq[type])); } -static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, bool reclaiming) +static inline bool __lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, + unsigned long scanned_seq, bool reclaiming) { unsigned long seq; unsigned long flags; @@ -347,6 +348,8 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, return false; seq = lru_gen_folio_seq(lruvec, folio, reclaiming); + if (scanned_seq != -1UL) + seq = max(seq, min(scanned_seq + 1, lrugen->max_seq)); gen = lru_gen_from_seq(seq); flags = (gen + 1UL) << LRU_GEN_PGOFF; /* see the comment on MIN_NR_GENS about PG_active */ @@ -362,6 +365,17 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, return true; } +static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, bool reclaiming) +{ + return __lru_gen_add_folio(lruvec, folio, -1UL, reclaiming); +} + +static inline bool lru_gen_add_rejected_folio(struct lruvec *lruvec, struct folio *folio, + unsigned long scanned_seq) +{ + return __lru_gen_add_folio(lruvec, folio, scanned_seq, false); +} + static inline bool lru_gen_del_folio(struct lruvec *lruvec, struct folio *folio, bool reclaiming) { unsigned long flags; @@ -420,6 +434,12 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, return false; } +static inline bool lru_gen_add_rejected_folio(struct lruvec *lruvec, struct folio *folio, + unsigned long scanned_seq) +{ + return false; +} + static inline bool lru_gen_del_folio(struct lruvec *lruvec, struct folio *folio, bool reclaiming) { return false; diff --git a/mm/vmscan.c b/mm/vmscan.c index 12aca97be56b..39f77a68be37 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1971,7 +1971,8 @@ static bool too_many_isolated(struct pglist_data *pgdat, int file, * * Note: The caller must not hold any lruvec lock. */ -static unsigned int move_folios_to_lru(struct list_head *list, bool do_rotate) +static unsigned int move_folios_to_lru(struct list_head *list, unsigned long seq, + bool do_rotate) { int nr_pages, nr_moved = 0; struct lruvec *lruvec = NULL; @@ -2028,7 +2029,7 @@ static unsigned int move_folios_to_lru(struct list_head *list, bool do_rotate) !folio_test_referenced(folio) && folio_ref_count(folio) == folio_expected_ref_count(folio)) lruvec_add_folio_tail(lruvec, folio); - else + else if (seq == -1UL || !lru_gen_add_rejected_folio(lruvec, folio, seq)) lruvec_add_folio(lruvec, folio); nr_pages = folio_nr_pages(folio); @@ -2147,7 +2148,7 @@ static unsigned long shrink_inactive_list(unsigned long nr_to_scan, nr_reclaimed = shrink_folio_list(&folio_list, pgdat, sc, &stat, false, lruvec_memcg(lruvec)); - move_folios_to_lru(&folio_list, true); + move_folios_to_lru(&folio_list, -1UL, true); mod_lruvec_state(lruvec, PGDEMOTE_KSWAPD + reclaimer_offset(sc), stat.nr_demoted); @@ -2258,8 +2259,8 @@ static void shrink_active_list(unsigned long nr_to_scan, /* * Move folios back to the lru list. */ - nr_activate = move_folios_to_lru(&l_active, false); - nr_deactivate = move_folios_to_lru(&l_inactive, false); + nr_activate = move_folios_to_lru(&l_active, -1UL, false); + nr_deactivate = move_folios_to_lru(&l_inactive, -1UL, false); count_vm_events(PGDEACTIVATE, nr_deactivate); count_memcg_events(lruvec_memcg(lruvec), PGDEACTIVATE, nr_deactivate); @@ -4910,7 +4911,8 @@ static bool isolate_folio(struct lruvec *lruvec, struct folio *folio, struct sca static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec, struct scan_control *sc, int type, int tier, - struct list_head *list, int *isolatedp) + struct list_head *list, int *isolatedp, + unsigned long *scanned_seq) { enum node_stat_item item; int zone_idx; @@ -4941,6 +4943,7 @@ static int scan_folios(unsigned long nr_to_scan, struct lruvec *lruvec, seq = lrugen->max_seq; seq = lruvec_populated_min_seq(lruvec, type, sc->reclaim_idx + 1, seq); + *scanned_seq = seq; gen = lru_gen_from_seq(seq); max_gen = lru_gen_from_seq(max_seq); @@ -5135,6 +5138,7 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec, int tier, scanned, reclaimed; int isolated = 0, nr_isolated = 0; unsigned long total_reclaimed = 0; + unsigned long scanned_seq; bool skip_retry = false; struct mem_cgroup *memcg = lruvec_memcg(lruvec); struct pglist_data *pgdat = lruvec_pgdat(lruvec); @@ -5146,7 +5150,7 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec, tier = get_tier_idx(lruvec, type); scanned = scan_folios(nr_to_scan, lruvec, sc, - type, tier, &list, &isolated); + type, tier, &list, &isolated, &scanned_seq); nr_isolated = isolated; if (nr_isolated) __mod_node_page_state(pgdat, NR_ISOLATED_ANON + type, @@ -5172,8 +5176,6 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec, type ? LRU_INACTIVE_FILE : LRU_INACTIVE_ANON); list_for_each_entry_safe_reverse(folio, next, &list, lru) { - DEFINE_MIN_SEQ(lruvec); - /* move_folios_to_lru() culls unevictable folios via folio_putback_lru() */ if (!folio_evictable(folio)) continue; @@ -5192,11 +5194,9 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec, * so this effectively promotes them by at least one generation. */ folio_set_lru_refs(folio, 0); - if (lru_gen_folio_seq(lruvec, folio, false) == min_seq[type]) - folio_set_active(folio); } - move_folios_to_lru(&list, false); + move_folios_to_lru(&list, scanned_seq, false); walk = current->reclaim_state->mm_walk; if (walk && walk->batched) { -- 2.34.1