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=1794693547; b=5KOAGGamdIauWhvgdkuES3Yh00Hho51mVKZQkVKRuiMgijSKw4JRRGWorn/nX+94L2Ii nrBWu330oxX+8R7BPOtd8I+TA6YAy9Rnqjx3j4NiDJCE68d7HOFjLVwpxQmjwWIiJxndm cnds1JukPn0bNNUa4m5L810vxg6vVsIrUgybZucAzZLg2wBXo3huQoApdYXrYD6jYELXW O80ohiPTnqIRoNqoZKkMQZrwkrLDZCEhsKVGdQLNd2dWpa8JMu8FHO4ZF2Qewlrn1NDQH kVPkGsCa+hmJ8lwrVHs7fKMU8xPbkzgAqT0NOUl4j/VTxVz8dNwwOJ896GIDjQ1LRXw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794693547; h=Received:DKIM-Signature:Date:To:From:Subject:Message-Id; bh=SQFrN+CO/9mKaInNzUJVl6HXu4dgPyIwC5vPaFc4sNw=; b=W3fYDyN+wJa6i/4aZp9mzpiESB9SPw3hcpPf61DdwC/0dEO/pbhMUXGLKFggftIO/Gtf ZsuVHhgltLemFVh0OwA4BlRihVubBTZfzwTMV1XHqp2U1HmiQC2mGMrafS7dxb+P6xC1C XOcQO3McEJuFVp3ptmdgByIl4sP8eDVoZtq3DVoC8/1aVBRwv+DIspHrDuYmmxnZjCMVz YAw/NOf1PSxao1oLU/vtCObc3At+cDiXnkric2qPd1tyucrH/uHYryif9q+M8yXQR685n nBzp/FkBDVf24R9UOmAF6RSywvYIfE0gPK397tpuggpiI3DVMB+ENTyx1k8wK16oqNA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=2Wy4gnZL; 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 3AF8F606A329 for ; Sat, 14 Nov 2026 21:59:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.a=rsa-sha256 header.s=korg header.b=2Wy4gnZL Received: by smtp.kernel.org (Postfix) with ESMTPSA id AEC651F000C4; Sat, 14 Nov 2026 21:59:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1794693546; bh=SQFrN+CO/9mKaInNzUJVl6HXu4dgPyIwC5vPaFc4sNw=; h=Date:To:From:Subject; b=2Wy4gnZLstgK87a0zH+0ive5QzOwfenCLItcXPgl+qJ2bKgX3DBjlmPsWf9wKhx9B 77hXgIPQrIcMOIRwyCGN50u9ouSgtrBUCB9wHF3T+h5mrmSDAH48Rt6i9RjVUyqzwZ A5b/rIwRKZ4g4bjjPeuUMDjLR+060HmKxnO3/Upc= Date: Sat, 14 Nov 2026 13:59:06 -0800 To: mm-commits@vger.kernel.org,kasong@tencent.com,akpm@linux-foundation.org From: Andrew Morton Subject: [to-be-updated] mm-mglru-reclaim-from-the-oldest-populated-gen.patch removed from -mm tree Message-Id: <20261114215906.AEC651F000C4@smtp.kernel.org> X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list The quilt patch titled Subject: mm/mglru: reclaim from the oldest populated gen has been removed from the -mm tree. Its filename was mm-mglru-reclaim-from-the-oldest-populated-gen.patch This patch was dropped because an updated version will be issued ------------------------------------------------------ From: Kairui Song Subject: mm/mglru: reclaim from the oldest populated gen Date: Sat, 14 Nov 2026 02:55:28 +0800 Currently MGLRU tries to keep the gen numbers of the two types in sync, avoiding reducing the gen number of one type when the other type has more gens, as described in the comment in try_to_inc_min_seq(). This makes scan_folios() stuck reclaiming the type with fewer gens: it always scanned the oldest gen of the type, even when that gen was empty, so reclaim made no progress on that type unless forced aging created a new gen and eliminated the dead empty gen. There are other approaches, like lifting the gen number synchronization [1]. However, that would break the gen layout used by lru_gen_folio_seq(): newly added folios would no longer have a well-defined hotness according to their gen number, which reduces accuracy. It is also not pressure-aware, since with gentle reclaim we still want to respect the gen layout (hotness). Instead, reclaim from whichever populated oldest gen is left, but only when the default reclaim priority can't satisfy the reclaimer's requirement. This is typical for swappiness limitations: e.g., low swappiness asks the reclaimer to reclaim from file, but file gens are drained, so the reclaim cycle fails and priority is raised. At the default priority the scan quota is 1/4096 of the evictable size, and the old behavior is kept there to respect the hotness distribution. Once priority is raised, the quota is at least 1/2048, so the hotness bias introduced by reclaiming from a younger gen is bounded by that quota, which seems fair. Global reclaim for MGLRU may start with DEF_PRIORITY / 2 (1/64); the ratio is still reasonable at that point, and when global pressure is more critical, we should reclaim harder. Note that scan_folios() still refuses to reclaim a type left with only MIN_NR_GENS gens, so a completely drained type still requires aging. This change only avoids scanning empty gens when populated reclaimable gens remain. Link: https://lore.kernel.org/20261113185541.70203-4-baohua@kernel.org Link: https://lore.kernel.org/linux-mm/20260726122123.7614-4-baohua@kernel.org/ [1] Signed-off-by: Kairui Song Signed-off-by: Barry Song Signed-off-by: Andrew Morton Reviewed-by: Kunwu Chan Cc: Axel Rasmussen Cc: Baolin Wang Cc: Baoquan He Cc: Johannes Weiner Cc: Cc: Liam R. Howlett Cc: wang lian Cc: Cc: Cc: Michal Hocko Cc: Qi Zheng Cc: Ridong Chen Cc: Mike Rapoport Cc: Kairui Song Cc: Shakeel Butt Cc: Suren Baghdasaryan Cc: wangzicheng Cc: Wei Xu Cc: Yuanchu Xie Cc: Bo Zhang Cc: Hui Zhu Cc: Siddharth Chintamaneni Cc: Kunwu Chan Cc: Bo Zhang --- mm/vmscan.c | 30 +++++++++++++++++++----------- 1 file changed, 19 insertions(+), 11 deletions(-) --- a/mm/vmscan.c~mm-mglru-reclaim-from-the-oldest-populated-gen +++ a/mm/vmscan.c @@ -3312,11 +3312,9 @@ static int __folio_inc_gen(struct folio } /* protect pages accessed multiple times through file descriptors */ -static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio) +static int folio_inc_gen(struct lruvec *lruvec, struct folio *folio, int old_gen) { - int type = folio_is_file_lru(folio); - struct lru_gen_folio *lrugen = &lruvec->lrugen; - int new_gen, old_gen = lru_gen_from_seq(lrugen->min_seq[type]); + int new_gen; bool gen_increased; new_gen = __folio_inc_gen(folio, old_gen, &gen_increased); @@ -4679,7 +4677,7 @@ void lru_gen_reparent_memcg(struct mem_c ******************************************************************************/ static bool sort_folio(struct lruvec *lruvec, struct folio *folio, struct scan_control *sc, - int tier_idx) + int min_gen, int tier_idx) { int gen = folio_lru_gen(folio); int type = folio_is_file_lru(folio); @@ -4697,14 +4695,14 @@ static bool sort_folio(struct lruvec *lr return false; /* promoted */ - if (gen != lru_gen_from_seq(lrugen->min_seq[type])) { + if (gen != min_gen) { list_move(&folio->lru, &lrugen->folios[gen][type][zone]); return true; } /* protected */ if (tier > tier_idx || refs + workingset == BIT(LRU_REFS_WIDTH) + 1) { - gen = folio_inc_gen(lruvec, folio); + gen = folio_inc_gen(lruvec, folio, min_gen); list_move(&folio->lru, &lrugen->folios[gen][type][zone]); /* don't count the workingset being lazily promoted */ @@ -4719,7 +4717,7 @@ static bool sort_folio(struct lruvec *lr /* ineligible */ if (zone > sc->reclaim_idx) { - gen = folio_inc_gen(lruvec, folio); + gen = folio_inc_gen(lruvec, folio, min_gen); list_move_tail(&folio->lru, &lrugen->folios[gen][type][zone]); return true; } @@ -4762,17 +4760,27 @@ static int scan_folios(unsigned long nr_ int scanned = 0; int isolated = 0; int skipped = 0; + unsigned long min_seq; unsigned long remaining = nr_to_scan; struct lru_gen_folio *lrugen = &lruvec->lrugen; VM_WARN_ON_ONCE(nr_to_scan > MAX_LRU_BATCH); VM_WARN_ON_ONCE(!list_empty(list)); + /* + * Respect the gen hotness distribution at low priority to avoid + * aging and scan cost, but prefer to satisfy the reclaimers request + * when under pressure to respect swappiness more and reduce IO cost. + */ + 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; - gen = lru_gen_from_seq(lrugen->min_seq[type]); - + gen = lru_gen_from_seq(min_seq); for (i = MAX_NR_ZONES; i > 0; i--) { LIST_HEAD(moved); int skipped_zone = 0; @@ -4790,7 +4798,7 @@ static int scan_folios(unsigned long nr_ scanned += delta; - if (sort_folio(lruvec, folio, sc, tier)) + if (sort_folio(lruvec, folio, sc, gen, tier)) sorted += delta; else if (isolate_folio(lruvec, folio, sc)) { list_add(&folio->lru, list); _ Patches currently in -mm which might be from kasong@tencent.com are mm-mglru-lift-the-forced-protection-of-reclaimer.patch mm-mglru-skip-zones-above-reclaim_idx-instead-of-rotating-them.patch mm-mglru-return-for-unavailable-anon-reclaim-earlier.patch mm-mglru-balance-anon-and-file-scan-budget-by-refault-rate.patch mm-mglru-lift-youngest-gen-protection-for-higher-priority.patch