From nobody Thu Sep 11 12:54:37 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 01872C05027 for ; Mon, 20 Feb 2023 09:17:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231510AbjBTJRe (ORCPT ); Mon, 20 Feb 2023 04:17:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57628 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231495AbjBTJRa (ORCPT ); Mon, 20 Feb 2023 04:17:30 -0500 Received: from mail-pl1-x631.google.com (mail-pl1-x631.google.com [IPv6:2607:f8b0:4864:20::631]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6659E1040A for ; Mon, 20 Feb 2023 01:17:04 -0800 (PST) Received: by mail-pl1-x631.google.com with SMTP id u17so678257plh.6 for ; Mon, 20 Feb 2023 01:17:04 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20210112.gappssmtp.com; s=20210112; t=1676884624; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=OSu6LoDi3bt+On14RPrDb/428OOXZNPo77LIFm1Bi28=; b=neiTcExIi57fl2R7QOvc3r3ELyzAtnMxW9GBNNCltkuMHmkXl5ZK+7Q0xCR6QpS+bt hP0XX6ZlR6iZxJOKblWlpeGKlK0XFXTJ6YTh8xf01BgvCpVSzBAdsU1eNWAu/zmWpkI3 9p1TCdObRxhi5YMuGSLQ1T3HSRXNro+TSsI76hsUHs5DW20YstK9espDPHnwdEXtao3l lajZuuPnoZK/Rm/vt/YViwwLTzZW/RtdXkdVPp+DvpozOWqhFL7zaeOqjL7CkS5IB/Uq XEBgboArtxfsBttqiHviM+ZB06ohsgBSRsBrlb3EsBlg+YZoeTyyZ3T9K3z2UfsI7PLd kbmA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1676884624; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=OSu6LoDi3bt+On14RPrDb/428OOXZNPo77LIFm1Bi28=; b=lWlbCcn+OqhK8MU6bYfP91TQ0BYoHIiFYrS/F6e/PCrJli3JxO2GgbIrXR/umFGk/r Xpkfe1wqAVzpV0lYI9W2+FCf7YskgR+1GttngZ2OnePEdtTHBXdNvUHwxcM1AVTRUibA zE+h6H40wdYrnsHtwG9B2Exh+sTzXs+T3Wp9StrajjQqk5VBGbeSrtkUOwLprX7gk8xJ dJphTIr5TypqLhCXjY/btJPxhrP1MTBxIRZ7n/TFO0FyckUlIkWOvFk9bur22t9Ro62z jCJsp3q/8rUrRLG1EPxrq8tOIDuAyn1SMi4eEOQJn7jFaj7sQ6PjOzrzWtmrx+UAI+Bo Pxag== X-Gm-Message-State: AO0yUKWOsgSfhDsIMVxSU9rCrCx2nJEE0it8KaR+kPLaIGQwXCe0xH9U LZyHBTC0Vk60rFVKIOFaiVTQlw== X-Google-Smtp-Source: AK7set/Qfx+rPSFCLub0/LUO6j0gUaT7gq5PlaRfKArK9fwOowwRmHnhYd2zrA9jqT1wfk9fQyhMBA== X-Received: by 2002:a17:90a:bf0d:b0:233:a836:15f4 with SMTP id c13-20020a17090abf0d00b00233a83615f4mr528696pjs.1.1676884623852; Mon, 20 Feb 2023 01:17:03 -0800 (PST) Received: from C02DW0BEMD6R.bytedance.net ([139.177.225.229]) by smtp.gmail.com with ESMTPSA id fs13-20020a17090af28d00b002339195a47bsm432382pjb.53.2023.02.20.01.16.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 20 Feb 2023 01:17:03 -0800 (PST) From: Qi Zheng To: akpm@linux-foundation.org, hannes@cmpxchg.org, shakeelb@google.com, mhocko@kernel.org, roman.gushchin@linux.dev, muchun.song@linux.dev, david@redhat.com, shy828301@gmail.com Cc: tkhai@ya.ru, sultan@kerneltoast.com, dave@stgolabs.net, penguin-kernel@I-love.SAKURA.ne.jp, paulmck@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Qi Zheng Subject: [PATCH 1/5] mm: vmscan: make global slab shrink lockless Date: Mon, 20 Feb 2023 17:16:33 +0800 Message-Id: <20230220091637.64865-2-zhengqi.arch@bytedance.com> X-Mailer: git-send-email 2.24.3 (Apple Git-128) In-Reply-To: <20230220091637.64865-1-zhengqi.arch@bytedance.com> References: <20230220091637.64865-1-zhengqi.arch@bytedance.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" The shrinker_rwsem is a global lock in shrinkers subsystem, it is easy to cause blocking in the following cases: a. the write lock of shrinker_rwsem was held for too long. For example, there are many memcgs in the system, which causes some paths to hold locks and traverse it for too long. (e.g. expand_shrinker_info()) b. the read lock of shrinker_rwsem was held for too long, and a writer came at this time. Then this writer will be forced to wait and block all subsequent readers. For example: - be scheduled when the read lock of shrinker_rwsem is held in do_shrink_slab() - some shrinker are blocked for too long. Like the case mentioned in the patchset[1]. Therefore, many times in history ([2],[3],[4],[5]), some people wanted to replace shrinker_rwsem reader with SRCU, but they all gave up because SRCU was not unconditionally enabled. But now, since commit 1cd0bd06093c ("rcu: Remove CONFIG_SRCU"), the SRCU is unconditionally enabled. So it's time to use SRCU to protect readers who previously held shrinker_rwsem. [1]. https://lore.kernel.org/lkml/20191129214541.3110-1-ptikhomirov@virtuoz= zo.com/ [2]. https://lore.kernel.org/all/1437080113.3596.2.camel@stgolabs.net/ [3]. https://lore.kernel.org/lkml/1510609063-3327-1-git-send-email-penguin-= kernel@I-love.SAKURA.ne.jp/ [4]. https://lore.kernel.org/lkml/153365347929.19074.12509495712735843805.s= tgit@localhost.localdomain/ [5]. https://lore.kernel.org/lkml/20210927074823.5825-1-sultan@kerneltoast.= com/ Signed-off-by: Qi Zheng --- mm/vmscan.c | 27 +++++++++++---------------- 1 file changed, 11 insertions(+), 16 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 9c1c5e8b24b8..95a3d6ddc6c1 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -202,6 +202,7 @@ static void set_task_reclaim_state(struct task_struct *= task, =20 LIST_HEAD(shrinker_list); DECLARE_RWSEM(shrinker_rwsem); +DEFINE_SRCU(shrinker_srcu); =20 #ifdef CONFIG_MEMCG static int shrinker_nr_max; @@ -699,7 +700,7 @@ void free_prealloced_shrinker(struct shrinker *shrinker) void register_shrinker_prepared(struct shrinker *shrinker) { down_write(&shrinker_rwsem); - list_add_tail(&shrinker->list, &shrinker_list); + list_add_tail_rcu(&shrinker->list, &shrinker_list); shrinker->flags |=3D SHRINKER_REGISTERED; shrinker_debugfs_add(shrinker); up_write(&shrinker_rwsem); @@ -753,13 +754,15 @@ void unregister_shrinker(struct shrinker *shrinker) return; =20 down_write(&shrinker_rwsem); - list_del(&shrinker->list); + list_del_rcu(&shrinker->list); shrinker->flags &=3D ~SHRINKER_REGISTERED; if (shrinker->flags & SHRINKER_MEMCG_AWARE) unregister_memcg_shrinker(shrinker); debugfs_entry =3D shrinker_debugfs_remove(shrinker); up_write(&shrinker_rwsem); =20 + synchronize_srcu(&shrinker_srcu); + debugfs_remove_recursive(debugfs_entry); =20 kfree(shrinker->nr_deferred); @@ -779,6 +782,7 @@ void synchronize_shrinkers(void) { down_write(&shrinker_rwsem); up_write(&shrinker_rwsem); + synchronize_srcu(&shrinker_srcu); } EXPORT_SYMBOL(synchronize_shrinkers); =20 @@ -989,6 +993,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int ni= d, { unsigned long ret, freed =3D 0; struct shrinker *shrinker; + int srcu_idx; =20 /* * The root memcg might be allocated even though memcg is disabled @@ -1000,10 +1005,10 @@ static unsigned long shrink_slab(gfp_t gfp_mask, in= t nid, if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg)) return shrink_slab_memcg(gfp_mask, nid, memcg, priority); =20 - if (!down_read_trylock(&shrinker_rwsem)) - goto out; + srcu_idx =3D srcu_read_lock(&shrinker_srcu); =20 - list_for_each_entry(shrinker, &shrinker_list, list) { + list_for_each_entry_srcu(shrinker, &shrinker_list, list, + srcu_read_lock_held(&shrinker_srcu)) { struct shrink_control sc =3D { .gfp_mask =3D gfp_mask, .nid =3D nid, @@ -1014,19 +1019,9 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int= nid, if (ret =3D=3D SHRINK_EMPTY) ret =3D 0; freed +=3D ret; - /* - * Bail out if someone want to register a new shrinker to - * prevent the registration from being stalled for long periods - * by parallel ongoing shrinking. - */ - if (rwsem_is_contended(&shrinker_rwsem)) { - freed =3D freed ? : 1; - break; - } } =20 - up_read(&shrinker_rwsem); -out: + srcu_read_unlock(&shrinker_srcu, srcu_idx); cond_resched(); return freed; } --=20 2.20.1