From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C8E693D7D6C for ; Fri, 31 Jul 2026 08:39:20 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785487162; cv=none; b=CQL6Wh5vMyNs6HdMv3aAc56IDSimF/Go6GyqzsrbGXTa8O/58yLkaW8n46SqzAfMzWgbCd6jNCwZAX1TBI/rQGfzcjtA0XKtz3tTf9qald35MvCinf/lmkdGaHWRqkKoKx7hLKW9mwddXaFdsJEmFacWyHmIyociRUrPmoBVCxw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785487162; c=relaxed/simple; bh=lZ94UIn6/gawFF/AaRI0gt80BUeBtN2i3lSBeKDIi+g=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=W/BlAL1yjgOPMV/T+QyqpUH0X1dWEtha7bR+/ZnTZv1GeyladojAkVagi0Nup7Thb1hbxV8Khq85x9AOjxaiWBjhF/eAO21Qp9QcpsXY/utLI1n3Hnm9q/D0U0NJK3fT6hxFqe1uamhD5jEksGyHCapnJMpf8Y8SfHw3EMNCOMM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=BqpESvbN; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="BqpESvbN" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 17D4F1F00A3D; Fri, 31 Jul 2026 08:39:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785487160; bh=ihmxc/uju4l+NYhonEwKFariUb9t7YQeSVnFbp6tBNE=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=BqpESvbNDFygmGxUmbtGwn2yI5In9LieGYe0mz4gyWc2pGlqVEWaKwrz5Gs1RxeHM t31hQRkpRcT+6o28KD7Mdoy4X+yKaRjtBY5HgINATIjTQ43ZfmTShoXd7cQzvyunOj u0DxEQX04D0c1Vhfqdhx/MFqPDWSuqvjHrSn+udwR68kPtHDXlFXZ9ieTMy26marnc HlySCWb7HtS3B9LPqpE2+3MyFwZV8ljPVo/e3Jz9DVhf0ELc7VFdVj89OsgVhS24Cl YyQEUWylSNGKWnPD5/an3hDnqTzRXmRmV+tnriR4ObTxIZ2X/2tq+yweasg8BajPn/ XeDbpfhkNDcdQ== From: "Barry Song (Xiaomi)" To: akpm@linux-foundation.org, linux-mm@kvack.org Cc: axelrasmussen@google.com, david@kernel.org, hannes@cmpxchg.org, kasong@tencent.com, linux-kernel@vger.kernel.org, ljs@kernel.org, lyugaofei@xiaomi.com, mhocko@kernel.org, qi.zheng@linux.dev, shakeel.butt@linux.dev, stevensd@chromium.org, weixugc@google.com, yuanchu@google.com, chenridong@xiaomi.com, zhangbo56@xiaomi.com, wangzicheng@honor.com, lianux.mm@gmail.com, Barry Song Subject: [RFC PATCH v3 5/6] mm: mglru: run aging when pages are severely imbalanced across gens Date: Fri, 31 Jul 2026 16:38:42 +0800 Message-Id: <20260731083843.37811-6-baohua@kernel.org> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20260731083843.37811-1-baohua@kernel.org> References: <20260731083843.37811-1-baohua@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: lyugaofei This partially restores the reclaim behavior introduced in Yu Zhao's initial MGLRU commit, ac35a4902370 ("mm: multi-gen LRU: minimal implementation"): /* * It's also ideal to spread pages out evenly, i.e., 1/(MIN_NR_GENS+1) * of the total number of pages for each generation. A reasonable range * for this average portion is [1/MIN_NR_GENS, 1/(MIN_NR_GENS+2)]. The * aging cares about the upper bound of hot pages, while the eviction * cares about the lower bound of cold pages. */ if (young * MIN_NR_GENS > total) return true; if (old * (MIN_NR_GENS + 2) < total) return true; But with a stricter condition: the younger generations must contain at least old_ratio times as many folios as the older generations. The old_ratio is derived from the lruvec size, so larger lruvecs use a higher old_ratio. This allows aging to keep folios of the preferred type distributed across the reclaimable generations. Also, imbalanced aging is only applied to non-balanced swappiness values (for example, < 60 or > 140). For balanced swappiness values near the middle, the swappiness bias is less of a concern, while the slightly increased aging overhead might be unacceptable. Signed-off-by: lyugaofei Co-developed-by: Barry Song (Xiaomi) Signed-off-by: Barry Song (Xiaomi) --- mm/vmscan.c | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 58 insertions(+), 1 deletion(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 2e7fef6975b6..98fd2fac90ac 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4973,9 +4973,62 @@ static int evict_folios(unsigned long nr_to_scan, struct lruvec *lruvec, return scanned; } +static inline bool swappiness_is_balanced(int swappiness) +{ + int range = MAX_SWAPPINESS - MIN_SWAPPINESS; + int middle = MIN_SWAPPINESS + range / 2; + + return swappiness >= middle - range / 5 && + swappiness <= middle + range / 5; +} + +static bool lru_gen_imbalanced(struct lruvec *lruvec, int type, + unsigned long max_seq, unsigned long min_seq, + struct scan_control *sc, int swappiness) +{ + struct lru_gen_folio *lrugen = &lruvec->lrugen; + unsigned long young = 0, old = 0, seq; + unsigned long old_ratio, gb; + + /* Skip swappiness bias for single-type reclaim or balanced swappiness */ + if (is_single_type_reclaim(swappiness) || swappiness_is_balanced(swappiness)) + return false; + + /* More than two generations remain to reclaim */ + if (min_seq + MIN_NR_GENS < max_seq) + return false; + + /* + * Run aging if the only remaining reclaimable generation + * has few folios. + */ + for (seq = min_seq; seq <= max_seq; seq++) { + int gen = lru_gen_from_seq(seq); + unsigned long size = 0; + int zone; + + for (zone = 0; zone < MAX_NR_ZONES; zone++) + size += max(READ_ONCE(lrugen->nr_pages[gen][type][zone]), 0L); + + if (seq + MIN_NR_GENS > max_seq) + young += size; + else + old += size; + } + /* + * Copied from inactive_is_low(), but uses a higher old_ratio to + * make aging less aggressive. + */ + gb = (young + old) >> (30 - PAGE_SHIFT); + old_ratio = gb ? int_sqrt(10 * gb) : 1; + old_ratio *= MAX_NR_GENS; + return young > old * old_ratio; +} + static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq, struct scan_control *sc, int swappiness) { + int type = get_type_to_scan(lruvec, swappiness); DEFINE_MIN_SEQ(lruvec); /* have to run aging, since eviction is not possible anymore */ @@ -4987,7 +5040,11 @@ static bool should_run_aging(struct lruvec *lruvec, unsigned long max_seq, return false; /* better to run aging even though eviction is still possible */ - return evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS == max_seq; + if (evictable_min_seq(min_seq, swappiness) + MIN_NR_GENS == max_seq) + return true; + + /* Run aging if the preferred type is severely imbalanced across gens */ + return lru_gen_imbalanced(lruvec, type, max_seq, min_seq[type], sc, swappiness); } static long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc, -- 2.34.1