From nobody Tue Feb 10 14:49:22 2026 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 4B756EB64D8 for ; Thu, 22 Jun 2023 09:06:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232184AbjFVJG4 (ORCPT ); Thu, 22 Jun 2023 05:06:56 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47800 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231831AbjFVJEV (ORCPT ); Thu, 22 Jun 2023 05:04:21 -0400 Received: from mail-pf1-x436.google.com (mail-pf1-x436.google.com [IPv6:2607:f8b0:4864:20::436]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3B25C49D6 for ; Thu, 22 Jun 2023 01:58:06 -0700 (PDT) Received: by mail-pf1-x436.google.com with SMTP id d2e1a72fcca58-668842bc50dso866526b3a.1 for ; Thu, 22 Jun 2023 01:58:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance.com; s=google; t=1687424243; x=1690016243; 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=A8Fm0YGxp8yCkyBdSSDbuW3Cqk4JmtEEZRGj6EeWqug=; b=VXm59oxeB5FguY23iZ6wxsHZUa/n0ixVM5+RJovFhBsSqk7jUN18WD75GpJCgArR0W JBsEkA9d39jtf7NG1SF+QvFe/XJdGOqobYaTEX0aq6YpeCNoIMMKV4Gdkmm7QKEFMCrH QNswdcRq+FKKLLJSUCefQDEwUuyAf6EXdUAA8SWzr8d5PlDWqAvD+NLb3ziu4Q1ZbddG 3AHOgUEiuKr4IMyzSNLNbfYcakjlWAem1FVIRkWrvCWnM54TEnQwCZtRjpDkJUyTk1gU FK042RTEuCbaP60yQQ0pKyvy7feFAoM0ianmMZaWx78B21cSO7WyFn4vwESs5Li+xEdq ozzg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1687424243; x=1690016243; 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=A8Fm0YGxp8yCkyBdSSDbuW3Cqk4JmtEEZRGj6EeWqug=; b=epDw6N5j3lEf0sDbf3Mq6Zw2Udld/C9Z47BW+fQLPyb6fDT9Lwq6JyFZ0VmUu7K092 o8sWf36rx4T5N+jltoKKZL3sYr2vSf9aHNJ6TL8nrXRybAb+wD+6WtTj0LAlTUPPh+Vz Hjv64/qwnNfDtearxlwArIVNxokaQ56Wn5EdzosndvBeW/Gb4b83SnnqtX8YNckeBx7g xCMSYmoEtzSbu1eQTlYG19QE92CP+Lc8J46yXr//sFC2iThQJDUCjiSbjN1VP3MXikAR J1kcoAqKbxd8iomlbv5rUw15GOU5jcN6djgQEqENLOgPHEE7OMxvSdhD6/V0kXhBjKa2 2tMg== X-Gm-Message-State: AC+VfDxb6dyifZZ8pwLv1sQqA7T2ji3JcAUqMqP0SWG5HhRni7LF9/Wx 4mkmupybbRQWu11Nd3rMu5f16Q== X-Google-Smtp-Source: ACHHUZ6zp07NG2bkXXxglRYaIEoFlfKXA7hhsSA7stt9xCgrqpdelrec/tU9od+DRY9y6jYGAzcstA== X-Received: by 2002:a17:902:da91:b0:1b0:3d54:358f with SMTP id j17-20020a170902da9100b001b03d54358fmr20812342plx.0.1687424243512; Thu, 22 Jun 2023 01:57:23 -0700 (PDT) Received: from C02DW0BEMD6R.bytedance.net ([139.177.225.254]) by smtp.gmail.com with ESMTPSA id h2-20020a170902f7c200b001b549fce345sm4806971plw.230.2023.06.22.01.57.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Jun 2023 01:57:23 -0700 (PDT) From: Qi Zheng To: akpm@linux-foundation.org, david@fromorbit.com, tkhai@ya.ru, vbabka@suse.cz, roman.gushchin@linux.dev, djwong@kernel.org, brauner@kernel.org, paulmck@kernel.org, tytso@mit.edu Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-arm-msm@vger.kernel.org, dm-devel@redhat.com, linux-raid@vger.kernel.org, linux-bcache@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-nfs@vger.kernel.org, linux-xfs@vger.kernel.org, linux-btrfs@vger.kernel.org, Qi Zheng Subject: [PATCH 25/29] mm: vmscan: make memcg slab shrink lockless Date: Thu, 22 Jun 2023 16:53:31 +0800 Message-Id: <20230622085335.77010-26-zhengqi.arch@bytedance.com> X-Mailer: git-send-email 2.24.3 (Apple Git-128) In-Reply-To: <20230622085335.77010-1-zhengqi.arch@bytedance.com> References: <20230622085335.77010-1-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" Like global slab shrink, this commit also uses refcount+RCU method to make memcg slab shrink lockless. We can reproduce the down_read_trylock() hotspot through the following script: ``` DIR=3D"/root/shrinker/memcg/mnt" do_create() { mkdir -p /sys/fs/cgroup/memory/test mkdir -p /sys/fs/cgroup/perf_event/test echo 4G > /sys/fs/cgroup/memory/test/memory.limit_in_bytes for i in `seq 0 $1`; do mkdir -p /sys/fs/cgroup/memory/test/$i; echo $$ > /sys/fs/cgroup/memory/test/$i/cgroup.procs; echo $$ > /sys/fs/cgroup/perf_event/test/cgroup.procs; mkdir -p $DIR/$i; done } do_mount() { for i in `seq $1 $2`; do mount -t tmpfs $i $DIR/$i; done } do_touch() { for i in `seq $1 $2`; do echo $$ > /sys/fs/cgroup/memory/test/$i/cgroup.procs; echo $$ > /sys/fs/cgroup/perf_event/test/cgroup.procs; dd if=3D/dev/zero of=3D$DIR/$i/file$i bs=3D1M count=3D1 & done } case "$1" in touch) do_touch $2 $3 ;; test) do_create 4000 do_mount 0 4000 do_touch 0 3000 ;; *) exit 1 ;; esac ``` Save the above script, then run test and touch commands. Then we can use the following perf command to view hotspots: perf top -U -F 999 [-g] 1) Before applying this patchset: 35.34% [kernel] [k] down_read_trylock 18.44% [kernel] [k] shrink_slab 15.98% [kernel] [k] pv_native_safe_halt 15.08% [kernel] [k] up_read 5.33% [kernel] [k] idr_find 2.71% [kernel] [k] _find_next_bit 2.21% [kernel] [k] shrink_node 1.29% [kernel] [k] shrink_lruvec 0.66% [kernel] [k] do_shrink_slab 0.33% [kernel] [k] list_lru_count_one 0.33% [kernel] [k] __radix_tree_lookup 0.25% [kernel] [k] mem_cgroup_iter - 82.19% 19.49% [kernel] [k] shrink_slab - 62.00% shrink_slab 36.37% down_read_trylock 15.52% up_read 5.48% idr_find 3.38% _find_next_bit + 0.98% do_shrink_slab 2) After applying this patchset: 46.83% [kernel] [k] shrink_slab 20.52% [kernel] [k] pv_native_safe_halt 8.85% [kernel] [k] do_shrink_slab 7.71% [kernel] [k] _find_next_bit 1.72% [kernel] [k] xas_descend 1.70% [kernel] [k] shrink_node 1.44% [kernel] [k] shrink_lruvec 1.43% [kernel] [k] mem_cgroup_iter 1.28% [kernel] [k] xas_load 0.89% [kernel] [k] super_cache_count 0.84% [kernel] [k] xas_start 0.66% [kernel] [k] list_lru_count_one - 65.50% 40.44% [kernel] [k] shrink_slab - 22.96% shrink_slab 13.11% _find_next_bit - 9.91% do_shrink_slab - 1.59% super_cache_count 0.92% list_lru_count_one We can see that the first perf hotspot becomes shrink_slab, which is what we expect. Signed-off-by: Qi Zheng --- mm/vmscan.c | 58 +++++++++++++++++++++++++++++++++++++---------------- 1 file changed, 41 insertions(+), 17 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 767569698946..357a1f2ad690 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -213,6 +213,12 @@ static struct shrinker_info *shrinker_info_protected(s= truct mem_cgroup *memcg, lockdep_is_held(&shrinker_rwsem)); } =20 +static struct shrinker_info *shrinker_info_rcu(struct mem_cgroup *memcg, + int nid) +{ + return rcu_dereference(memcg->nodeinfo[nid]->shrinker_info); +} + static int expand_one_shrinker_info(struct mem_cgroup *memcg, int map_size, int defer_size, int old_map_size, int old_defer_size, @@ -339,7 +345,7 @@ void set_shrinker_bit(struct mem_cgroup *memcg, int nid= , int shrinker_id) struct shrinker_info *info; =20 rcu_read_lock(); - info =3D rcu_dereference(memcg->nodeinfo[nid]->shrinker_info); + info =3D shrinker_info_rcu(memcg, nid); if (!WARN_ON_ONCE(shrinker_id >=3D info->map_nr_max)) { /* Pairs with smp mb in shrink_slab() */ smp_mb__before_atomic(); @@ -359,7 +365,6 @@ static int prealloc_memcg_shrinker(struct shrinker *shr= inker) return -ENOSYS; =20 down_write(&shrinker_rwsem); - /* This may call shrinker, so it must use down_read_trylock() */ id =3D idr_alloc(&shrinker_idr, shrinker, 0, 0, GFP_KERNEL); if (id < 0) goto unlock; @@ -392,18 +397,28 @@ static long xchg_nr_deferred_memcg(int nid, struct sh= rinker *shrinker, struct mem_cgroup *memcg) { struct shrinker_info *info; + long nr_deferred; =20 - info =3D shrinker_info_protected(memcg, nid); - return atomic_long_xchg(&info->nr_deferred[shrinker->id], 0); + rcu_read_lock(); + info =3D shrinker_info_rcu(memcg, nid); + nr_deferred =3D atomic_long_xchg(&info->nr_deferred[shrinker->id], 0); + rcu_read_unlock(); + + return nr_deferred; } =20 static long add_nr_deferred_memcg(long nr, int nid, struct shrinker *shrin= ker, struct mem_cgroup *memcg) { struct shrinker_info *info; + long nr_deferred; + + rcu_read_lock(); + info =3D shrinker_info_rcu(memcg, nid); + nr_deferred =3D atomic_long_add_return(nr, &info->nr_deferred[shrinker->i= d]); + rcu_read_unlock(); =20 - info =3D shrinker_info_protected(memcg, nid); - return atomic_long_add_return(nr, &info->nr_deferred[shrinker->id]); + return nr_deferred; } =20 void reparent_shrinker_deferred(struct mem_cgroup *memcg) @@ -955,19 +970,18 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask= , int nid, { struct shrinker_info *info; unsigned long ret, freed =3D 0; - int i; + int i =3D 0; =20 if (!mem_cgroup_online(memcg)) return 0; =20 - if (!down_read_trylock(&shrinker_rwsem)) - return 0; - - info =3D shrinker_info_protected(memcg, nid); +again: + rcu_read_lock(); + info =3D shrinker_info_rcu(memcg, nid); if (unlikely(!info)) goto unlock; =20 - for_each_set_bit(i, info->map, info->map_nr_max) { + for_each_set_bit_from(i, info->map, info->map_nr_max) { struct shrink_control sc =3D { .gfp_mask =3D gfp_mask, .nid =3D nid, @@ -982,6 +996,10 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask,= int nid, continue; } =20 + if (!shrinker_try_get(shrinker)) + continue; + rcu_read_unlock(); + /* Call non-slab shrinkers even though kmem is disabled */ if (!memcg_kmem_online() && !(shrinker->flags & SHRINKER_NONSLAB)) @@ -1014,13 +1032,19 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_ma= sk, int nid, } freed +=3D ret; =20 - if (rwsem_is_contended(&shrinker_rwsem)) { - freed =3D freed ? : 1; - break; - } + shrinker_put(shrinker); + + /* + * We have already exited the read-side of rcu critical section + * before calling do_shrink_slab(), the shrinker_info may be + * released in expand_one_shrinker_info(), so restart the + * iteration. + */ + i++; + goto again; } unlock: - up_read(&shrinker_rwsem); + rcu_read_unlock(); return freed; } #else /* CONFIG_MEMCG */ --=20 2.30.2