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=1794439619; b=rtx24LujRhi04RSOpo/Ei+Hv/z8iVD8IyTMMQPnYtqHQaBuC+kXMIAIoVJohnHSN4XsS 2L5hICb+PBHDO/C09MmlF4zk7pyr1l8U806qw1L8P16MvQR2o1xoWi/rgQZ+rmYmFDu+y WyrfSp9JLUydAjt+v/y/1gG8T1dxP15AXu15RZ9zgj1WDBaex8z2SteeSGc4WQm1nzdYh MRZ2RUqUblRxBoRX1np0BK5rwqFWjE8SI31DD8wf6ADtR9qv2BVpj5DQlC+sRHXGRhoPs FO4t4MuSystmbjt5kKrDsxSLjVr5Cn8JLj9Oepu/SXasSkJhrD5KC2ShntGVyacBkYA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794439619; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-Id:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=FJxYHKJjwXKsu2hlwRaRpHsizHesobIZOm9pboS/Wn4=; b=Lko9GsDRnSMY8jKiDd1/gxDXkTkHhCLftj+RgDKOdeoA17XfZiQZlJZsmws7yA4RwmmI NDun4yQdhm/5A34gVSY9wawbb7coC4HemCBYrRKl13mh0Jzr4qJoOyjLc4eiumzK9mwrh cBkn2/Va6cAf5vGaIfptgwT4xslXJcYBt7+jwzoZjdlJzqlcVmq51iQP6ncszgpbt6VUG ealoYW+vsLyCAtm2psGoXv7RPggAvGAT347hUnve9D5zBhKc2OjlTOVDEjz9BGy8Yvore HOy8YA3hLPCgHFXO/YUeIu0a/dNcN211R0Xrov49ctaQB+UIbxxZHzfH9P6dDg7ID/w== 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="YbjhB/hf"; 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 E797B606A887 for ; Wed, 11 Nov 2026 23:26:58 +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=YbjhB/hf Received: by smtp.kernel.org (Postfix) with ESMTPSA id B32301F00A05; Wed, 11 Nov 2026 23:26:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794439618; bh=FJxYHKJjwXKsu2hlwRaRpHsizHesobIZOm9pboS/Wn4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=YbjhB/hfjup11wsQFRtDV1m9sJwxcn+/JrqA+rMeex5Qe2ZAYXFrUUYjuAQ3SwdBj 3c/IXt2IL5MCvVa8lPUOmA9b7tHFOnP0ioYzyZoZHU+DQgejo+N+tRceksZi9Vcjzc h30/CHx4n8ZUKGQvXTTHzDtS7QmjmqlJ0C3Y7RHQQJdYUNPXrFXT24TrcC3Tdp7F17 gN4t2A1nccE0cgvSxITDdV/9MSrzzYCDsbBcDgwPOMjs8Pt3xhULOBDS25VdKRI01I 7RChjCqLEmlYLdm5xFllSY8ONXx95iKvP2yG8uiV61C18fM1qPQjL3pXB4uQlILVc0 O23lb8rCI9yKg== 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 (Xiaomi)" Subject: [PATCH v7 09/16] mm/mglru: Avoid placing rejected folios below populated gen Date: Thu, 12 Nov 2026 07:25:56 +0800 Message-Id: <20261111232603.9934-10-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 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) Reviewed-by: Kunwu Chan --- 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 da04d81a819c..0a055a3fe210 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 fff7ee17eb0d..c5c4d6418d46 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1864,7 +1864,8 @@ 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; @@ -1921,7 +1922,7 @@ 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); @@ -2040,7 +2041,7 @@ 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); @@ -2151,8 +2152,8 @@ 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); @@ -4748,7 +4749,8 @@ 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; @@ -4779,6 +4781,7 @@ 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); @@ -4975,6 +4978,7 @@ 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); @@ -4986,7 +4990,7 @@ 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, @@ -5012,8 +5016,6 @@ 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; @@ -5032,11 +5034,9 @@ 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