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Tue, 28 Feb 2023 02:11:42 -0800 (PST) Received: from [10.70.252.135] ([139.177.225.229]) by smtp.gmail.com with ESMTPSA id b8-20020aa78708000000b005a8ce67874asm5694754pfo.86.2023.02.28.02.11.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Feb 2023 02:11:42 -0800 (PST) Message-ID: Date: Tue, 28 Feb 2023 18:11:34 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.7.2 Subject: Re: [PATCH v3 0/8] make slab shrink lockless Content-Language: en-US To: Roman Gushchin 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 References: <20230226144655.79778-1-zhengqi.arch@bytedance.com> <20230226115100.7e12bda7931dd65dbabcebe3@linux-foundation.org> From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: u8t4xb96f8nj8j7h1w54onxj8pxu7csw X-Rspamd-Queue-Id: 0320F20016 X-HE-Tag: 1677579103-997115 X-HE-Meta: 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 p7b0exlS v/+Hht9z9QnYm3EuiWrNg/PHPx8axSvyzcu/fKrPfTYnJkurTZzGA8TufUTykjxU/1foTb9uCUQuM9AKo6gm54Rd77dRefeAFGFUlRjAOmTH+1KiOVPB3M5wLZBnfxVEgDExcA3O1dIupf7PEpOycpF8pV3rSRrVg/3kVbLTA99qTHtBJqo2nQ191dsLj5O6wsHi9pn1Df5G/n1jsJHNSkZ6rCQKYF7YNtIwisTVlFM1LMKxtB9nJkCDHWRe21Duyj0Xs2z+levR5XG8rOkIUI2z23AKXutj77vTNv7tPi3/TnNh7+hPr1zoNGcSNbK+XeUGpXrdh3j42kodvCbD/9ZTv51NnQx6oNBOQY9K1OMypIB+Xf3si7gbpdH15ER/sjd1Z5uVH/CLi2Q+zKp4whVXAxz1oPkllQZu7vEuVzMv0JVFZ1ZNz50q9/Q== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000010, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2023/2/28 03:02, Roman Gushchin wrote: > 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. Yes, in the above scenario, there is indeed no lock contention problem. > > 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! -- Thanks, Qi