From nobody Fri Sep 12 06:31:16 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D3CEEC636CC for ; Mon, 13 Feb 2023 07:53:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229877AbjBMHx2 (ORCPT ); Mon, 13 Feb 2023 02:53:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43416 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229436AbjBMHx1 (ORCPT ); Mon, 13 Feb 2023 02:53:27 -0500 Received: from mail-yw1-x1149.google.com (mail-yw1-x1149.google.com [IPv6:2607:f8b0:4864:20::1149]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4A0BA422A for ; Sun, 12 Feb 2023 23:53:26 -0800 (PST) Received: by mail-yw1-x1149.google.com with SMTP id 00721157ae682-52f233aff21so17929997b3.7 for ; Sun, 12 Feb 2023 23:53:26 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:from:subject:mime-version:message-id:date:from:to:cc:subject :date:message-id:reply-to; bh=NvhGAhuoLUXZRBDLvVFPku75YEeAYrautV9kwkbVm+U=; b=optKyx+Ol4vgXo9n9HECwvIRntjr3OUydQJaoxkHSsFuotk0exbyE/mdWNa18ffL/h qQmFuqJAhnLXTtEyCMP8wNz4mAakzwVU4q94mV8Eb8IFVJ+0aBHIa2GtgstgoQ8rRmle ZwjA6uZ6kVYx40fca2ORN7hr4T6JZTiBfUmY6DSxVTlpg4FGiulHGtFN3JM6VHlNRDyI PFoiyLYbHEbYKeXi7+LuOUPsT0PxNlbMuZH8JZiwTJ/vQ5GyrmGG4E2PlXIKAbHUWLhh Zlxp5yjsxYzXDqxwf8kdiOk1LJk33G+qspbVqUpAPZGKN3VTQA32H1LgXhuK0fIJHmI0 5PrQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:from:subject:mime-version:message-id:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=NvhGAhuoLUXZRBDLvVFPku75YEeAYrautV9kwkbVm+U=; b=OxbF3e+qWo6XbqDQNoKRnURA49TfkRCTZV7Cb3LUY6wey9UI67Sqn3tFUOkiSNpAIx zfKBRd0UJpOGLihKIXHuIWKHFrMTX35bni4vxj3l1OK5cU/Fwlk9sxmIN9OPjKv5O87p spA5VHu6uQwBAhmTmJOL5AW+vrJMM0F/799/BxzYFJ1FdrGZoUYIW1PS/HYsdppqa5k3 kv38JB3mFt+5pnLcN+BF52cVKY4rlk2V10WuRUBYEw/93/cNEyIKQGoZubGbiLHknfFv zYFZXii9T9Idrcxmcd4SoXIzdTi4pdadykscbeB88PxTIRSIVr/CpV30FXKeMRnRqqmh mX5w== X-Gm-Message-State: AO0yUKVRox6RPgvQto0IEhdZCc7wl8uIeM2z5R12AoZCSsh8NVU23yAg rGC0q+P7O/w0cU4/6SI9zQ82UBdeKOg= X-Google-Smtp-Source: AK7set/guU6artniwycMRZB/B3vkY/jJjJNmh0MMnseMPOIWtKnpO+3lWWTtlzgawUqAURmh5dclb/fIQ84= X-Received: from yuzhao.bld.corp.google.com ([2620:15c:183:200:7197:d392:1707:74d9]) (user=yuzhao job=sendgmr) by 2002:a81:a10:0:b0:521:daa4:d687 with SMTP id 16-20020a810a10000000b00521daa4d687mr30ywk.0.1676274805040; Sun, 12 Feb 2023 23:53:25 -0800 (PST) Date: Mon, 13 Feb 2023 00:53:22 -0700 Message-Id: <20230213075322.1416966-1-yuzhao@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.39.1.581.gbfd45094c4-goog Subject: [PATCH mm-unstable v1] mm: multi-gen LRU: avoid futile retries From: Yu Zhao To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-mm@google.com, Yu Zhao , "T . J . Mercier" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Recall that the per-node memcg LRU has two generations and they alternate when the last memcg (of a given node) is moved from one to the other. Each generation is also sharded into multiple bins to improve scalability. A reclaimer starts with a random bin (in the old generation) and, if it fails, it will retry, i.e., to try the rest of the bins. If a reclaimer fails with the last memcg, it should move this memcg to the young generation first, which causes the generations to alternate, and then retry. Otherwise, the retries will be futile because all other bins are empty. Fixes: e4dde56cd208 ("mm: multi-gen LRU: per-node lru_gen_folio lists") Reported-by: T.J. Mercier Signed-off-by: Yu Zhao --- mm/vmscan.c | 25 +++++++++++++++---------- 1 file changed, 15 insertions(+), 10 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index d4b9fd1ae0ed..34535bbd4fe9 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -5356,18 +5356,20 @@ static int shrink_one(struct lruvec *lruvec, struct= scan_control *sc) =20 static void shrink_many(struct pglist_data *pgdat, struct scan_control *sc) { + int op; int gen; int bin; int first_bin; struct lruvec *lruvec; struct lru_gen_folio *lrugen; + struct mem_cgroup *memcg; const struct hlist_nulls_node *pos; - int op =3D 0; - struct mem_cgroup *memcg =3D NULL; unsigned long nr_to_reclaim =3D get_nr_to_reclaim(sc); =20 bin =3D first_bin =3D get_random_u32_below(MEMCG_NR_BINS); restart: + op =3D 0; + memcg =3D NULL; gen =3D get_memcg_gen(READ_ONCE(pgdat->memcg_lru.seq)); =20 rcu_read_lock(); @@ -5391,14 +5393,22 @@ static void shrink_many(struct pglist_data *pgdat, = struct scan_control *sc) =20 op =3D shrink_one(lruvec, sc); =20 - if (sc->nr_reclaimed >=3D nr_to_reclaim) - goto success; - rcu_read_lock(); + + if (sc->nr_reclaimed >=3D nr_to_reclaim) + break; } =20 rcu_read_unlock(); =20 + if (op) + lru_gen_rotate_memcg(lruvec, op); + + mem_cgroup_put(memcg); + + if (sc->nr_reclaimed >=3D nr_to_reclaim) + return; + /* restart if raced with lru_gen_rotate_memcg() */ if (gen !=3D get_nulls_value(pos)) goto restart; @@ -5407,11 +5417,6 @@ static void shrink_many(struct pglist_data *pgdat, s= truct scan_control *sc) bin =3D get_memcg_bin(bin + 1); if (bin !=3D first_bin) goto restart; -success: - if (op) - lru_gen_rotate_memcg(lruvec, op); - - mem_cgroup_put(memcg); } =20 static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_contr= ol *sc) --=20 2.39.1.581.gbfd45094c4-goog