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From: Roman Gushchin To: Qi Zheng Cc: Andrew Morton , tkhai@ya.ru, hannes@cmpxchg.org, shakeelb@google.com, mhocko@kernel.org, muchun.song@linux.dev, david@redhat.com, shy828301@gmail.com, 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 Subject: Re: [PATCH v3 0/8] make slab shrink lockless Message-ID: References: <20230226144655.79778-1-zhengqi.arch@bytedance.com> <20230226115100.7e12bda7931dd65dbabcebe3@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: ax6hpfcoqkpe9xb4rmc8hiarzmgwizbb X-Rspamd-Queue-Id: 11941A0009 X-HE-Tag: 1677524551-429758 X-HE-Meta: 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 YD25tRud ihI8qZQZMQ4F9gafA9Gnb7R5pbxCHwbVS2WAlsv+FjtQQkrgR2gy4n9MP/ZFrKP/i1Gi1zk3X88MJvefXt+zYvv09GPU2lrRBXVB3PuriBP9rbs/L1f6bv2TX4jWwhXZHK2c8Rr2TItHhLDE3KPAi+dE9srzEeb+1BOMn 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 Mon, Feb 27, 2023 at 09:31:51PM +0800, Qi Zheng wrote: > > > On 2023/2/27 03:51, Andrew Morton wrote: > > On Sun, 26 Feb 2023 22:46:47 +0800 Qi Zheng wrote: > > > 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 > > 1) Before applying this patchset: > > 32.31% [kernel] [k] down_read_trylock > 19.40% [kernel] [k] pv_native_safe_halt > 16.24% [kernel] [k] up_read > 15.70% [kernel] [k] shrink_slab > 4.69% [kernel] [k] _find_next_bit > 2.62% [kernel] [k] shrink_node > 1.78% [kernel] [k] shrink_lruvec > 0.76% [kernel] [k] do_shrink_slab > > 2) After applying this patchset: > > 27.83% [kernel] [k] _find_next_bit > 16.97% [kernel] [k] shrink_slab > 15.82% [kernel] [k] pv_native_safe_halt > 9.58% [kernel] [k] shrink_node > 8.31% [kernel] [k] shrink_lruvec > 5.64% [kernel] [k] do_shrink_slab > 3.88% [kernel] [k] mem_cgroup_iter Not opposing the intention of the patchset in any way (I actually think it's a good idea to make the shrinkers list lockless), but looking at both outputs above I think that the main problem is not the contention on the semaphore, but the reason of this contention. It seems like often there is a long list of shrinkers which barely can reclaim any memory, but we're calling them again and again. In order to achieve real wins with real-life workloads, I guess it's what we should optimize. Thanks!