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Mon, 24 Jul 2023 20:01:21 -0700 (PDT) Received: from [10.70.252.135] ([203.208.167.147]) by smtp.gmail.com with ESMTPSA id fe15-20020a056a002f0f00b0066ccb8e8024sm8472563pfb.30.2023.07.24.20.01.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 24 Jul 2023 20:01:20 -0700 (PDT) Message-ID: <9b149dd9-1617-9af4-4252-6d0df01f93b1@bytedance.com> Date: Tue, 25 Jul 2023 11:01:06 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.12.0 Subject: Re: [PATCH v2 03/47] mm: shrinker: add infrastructure for dynamically allocating shrinker Content-Language: en-US To: Peter Zijlstra Cc: 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, steven.price@arm.com, cel@kernel.org, senozhatsky@chromium.org, yujie.liu@intel.com, gregkh@linuxfoundation.org, muchun.song@linux.dev, linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, kvm@vger.kernel.org, xen-devel@lists.xenproject.org, linux-erofs@lists.ozlabs.org, linux-f2fs-devel@lists.sourceforge.net, cluster-devel@redhat.com, linux-nfs@vger.kernel.org, linux-mtd@lists.infradead.org, rcu@vger.kernel.org, netdev@vger.kernel.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-xfs@vger.kernel.org, linux-btrfs@vger.kernel.org References: <20230724094354.90817-1-zhengqi.arch@bytedance.com> <20230724094354.90817-4-zhengqi.arch@bytedance.com> <20230724122549.GA3731903@hirez.programming.kicks-ass.net> From: Qi Zheng In-Reply-To: <20230724122549.GA3731903@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: DD4351A000D X-Stat-Signature: 4y5s61m3gim56ucnz79k8knkm4sdhtxz X-HE-Tag: 1690254082-95736 X-HE-Meta: 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 5NzO7lYI +TU1ZlueVkv79N5FXkfwct6wuE7l/9/ENiswdCD9cyBtPj8D7VEMmxy1DtaM8+Y5V/XalGyQ/s+a2GPUE6y44O99O3x+Vk6l8SbLpotPd/mt3uX1ccqxjw8VDdOravfUO6VnvimJKx7M17skoNiCCv63UZ2dB0qPAyNSZTOHZu+kJCu1YomR5RJamp0NGLCYbaL+5SoTVy82LHptpQ1JbAS1HaapOzt43RKQb7qcbE0SHHbMkKOc7gkZrVsw9S+RYlSB+Hn7GGf+ztqZJE9arSGBkS5AFQuBTRi4CAOf7zMQZrSs9AG/qIni5bUfvE4gx0JOSijxWjAD8Q+yUEB0JC2cUQzCfw5K8+zuR1mtPVPiXPnO3ZIelnpxLwA== 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: Hi Peter, On 2023/7/24 20:25, Peter Zijlstra wrote: > On Mon, Jul 24, 2023 at 05:43:10PM +0800, Qi Zheng wrote: > >> +void shrinker_unregister(struct shrinker *shrinker) >> +{ >> + struct dentry *debugfs_entry; >> + int debugfs_id; >> + >> + if (!shrinker || !(shrinker->flags & SHRINKER_REGISTERED)) >> + return; >> + >> + down_write(&shrinker_rwsem); >> + list_del(&shrinker->list); >> + shrinker->flags &= ~SHRINKER_REGISTERED; >> + if (shrinker->flags & SHRINKER_MEMCG_AWARE) >> + unregister_memcg_shrinker(shrinker); >> + debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id); >> + up_write(&shrinker_rwsem); >> + >> + shrinker_debugfs_remove(debugfs_entry, debugfs_id); > > Should there not be an rcu_barrier() right about here? The shrinker_debugfs_remove() will wait for debugfs_file_put() to return, so when running here, all shrinker debugfs operations have been completed. And the slab shrink will hold the read lock of shrinker_rwsem to traverse the shrinker_list, so when we hold the write lock of shrinker_rwsem to delete the shrinker from the shrinker_list, the shrinker will not be executed again. So I think there is no need to add a rcu_barrier() here. Please let me know if I missed something. Thanks, Qi > >> + >> + kfree(shrinker->nr_deferred); >> + shrinker->nr_deferred = NULL; >> + >> + kfree(shrinker); >> +} >> +EXPORT_SYMBOL(shrinker_unregister); >