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Thu, 28 Jul 2022 11:43:14 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id JI6lF1J24mL/EgAAMHmgww (envelope-from ); Thu, 28 Jul 2022 11:43:14 +0000 Date: Thu, 28 Jul 2022 13:43:13 +0200 From: Michal Hocko To: tujinjiang@bytedance.com Cc: shy828301@gmail.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2] vmscan: Do not free nr_deferred for memcg aware shrinkers Message-ID: References: <20220728091341.20820-1-tujinjiang@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220728091341.20820-1-tujinjiang@bytedance.com> ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1659008596; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; 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spf=pass (imf23.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com X-Rspamd-Server: rspam06 X-HE-Tag: 1659008595-251617 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu 28-07-22 17:13:41, tujinjiang@bytedance.com wrote: > From: Jinjiang Tu > > When a memcg aware shrinker is registered by register_shrinker(), > shrinker->nr_deferred will not be initialized. But when the shrinker > is unregistered by unregister_shrinker(), shrinker->nr_deferred > will be freed. > > Luckily, the memcg aware shrinkers in the current kernel are pre-zeroed. > But a new memcg aware shrinker may be added in the future, and we should > not assume the shrinker is pre-zeroed. > > Another unregister API free_prealloced_shrinker() does not assume the > shrinker is pre-zered and free shrinker->nr_deferred only if it is > not memcg aware. So unregister_shrinker() should do like > free_prealloced_shrinker(). > > Signed-off-by: Jinjiang Tu > --- > mm/vmscan.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index f7d9a683e3a7..f8a9a5349b6e 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -675,8 +675,11 @@ void unregister_shrinker(struct shrinker *shrinker) > down_write(&shrinker_rwsem); > list_del(&shrinker->list); > shrinker->flags &= ~SHRINKER_REGISTERED; > - if (shrinker->flags & SHRINKER_MEMCG_AWARE) > + if (shrinker->flags & SHRINKER_MEMCG_AWARE) { > unregister_memcg_shrinker(shrinker); > + up_write(&shrinker_rwsem); > + return; > + } > up_write(&shrinker_rwsem); > > kfree(shrinker->nr_deferred); Can we get rid of the code duplication? --- diff --git a/mm/vmscan.c b/mm/vmscan.c index f7d9a683e3a7..308279414fe8 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -632,12 +632,10 @@ int prealloc_shrinker(struct shrinker *shrinker) return 0; } -void free_prealloced_shrinker(struct shrinker *shrinker) +static void __free_shrinker(struct shrinker *shrinker) { if (shrinker->flags & SHRINKER_MEMCG_AWARE) { - down_write(&shrinker_rwsem); unregister_memcg_shrinker(shrinker); - up_write(&shrinker_rwsem); return; } @@ -645,6 +643,13 @@ void free_prealloced_shrinker(struct shrinker *shrinker) shrinker->nr_deferred = NULL; } +void free_prealloced_shrinker(struct shrinker *shrinker) +{ + down_write(&shrinker_rwsem); + __free_shrinker(shrinker); + up_write(&shrinker_rwsem); +} + void register_shrinker_prepared(struct shrinker *shrinker) { down_write(&shrinker_rwsem); @@ -675,12 +680,9 @@ void unregister_shrinker(struct shrinker *shrinker) down_write(&shrinker_rwsem); list_del(&shrinker->list); shrinker->flags &= ~SHRINKER_REGISTERED; - if (shrinker->flags & SHRINKER_MEMCG_AWARE) - unregister_memcg_shrinker(shrinker); - up_write(&shrinker_rwsem); - kfree(shrinker->nr_deferred); - shrinker->nr_deferred = NULL; + __free_shrinker(shrinker); + up_write(&shrinker_rwsem); } EXPORT_SYMBOL(unregister_shrinker); -- Michal Hocko SUSE Labs