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Mon, 27 Feb 2023 05:31:59 -0800 (PST) Received: from [10.70.252.135] ([139.177.225.229]) by smtp.gmail.com with ESMTPSA id c24-20020aa78c18000000b00593adee79efsm4220877pfd.55.2023.02.27.05.31.53 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 27 Feb 2023 05:31:59 -0800 (PST) Message-ID: Date: Mon, 27 Feb 2023 21:31:51 +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: Andrew Morton Cc: tkhai@ya.ru, hannes@cmpxchg.org, shakeelb@google.com, mhocko@kernel.org, roman.gushchin@linux.dev, 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: <20230226115100.7e12bda7931dd65dbabcebe3@linux-foundation.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 6457D1C0009 X-Stat-Signature: y5difteedgt45n1etyda9md6br54iq5x X-Rspam-User: X-HE-Tag: 1677504721-123108 X-HE-Meta: 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 reBvU4Ss 0cusn4XVEoRVCHcdiP53e92oSkEcrRg5imBYx0ZGVB9C5DIfxxZX4p5aC0a1BYDfXzSdVpCBKUzIS1+C47kDtoY1rs7iZTMLr4nXaHvxWbOdded9DGEfn33VRBwROQwKA/guY4Z1sEvXDeCKShO0VLx6zUN9sKwcx9040K3+XbRo4e3apCjgGyOo0gZtczzOn2Ygrw3ggukbSuaP8dBB4sXV7l/G/UpxIGlvGbJxmX3lVshdy8tfGEOQ4MqyzRMaAzv1hb7fj9g2nts+wGSu8/ACel7PAXCxLeonVS43OlSYk20LVyHzElov/2iYfCkpghYu6KIx3AkQqZ2OpL/ImiI/akGK6Rq70M87H2q5sWJiw6o1WnazH/4aeidT0Bn/2hwfdEcFYWXE2sfdPRVfn/Po2UOrks+jTmiYhILy7hribpV8unA6nsuNHWw== 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 2023/2/27 03:51, Andrew Morton wrote: > On Sun, 26 Feb 2023 22:46:47 +0800 Qi Zheng wrote: > >> Hi all, >> >> This patch series aims to make slab shrink lockless. > > What an awesome changelog. > >> 2. Survey >> ========= > > Especially this part. > > Looking through all the prior efforts and at this patchset I am not > immediately seeing any statements about the overall effect upon > real-world workloads. For a good example, does this patchset > measurably improve throughput or energy consumption on your servers? Hi Andrew, I re-tested with the following physical machines: Architecture: x86_64 CPU(s): 96 On-line CPU(s) list: 0-95 Model name: Intel(R) Xeon(R) Platinum 8260 CPU @ 2.40GHz I found that the reason for the hotspot I described in cover letter is wrong. The reason for the down_read_trylock() hotspot is not because of the failure to trylock, but simply because of the atomic operation (cmpxchg). And this will lead to a significant reduction in IPC (insn per cycle). To verify this, I did the following tests: 1. Run the following script to create down_read_trylock() hotspots: ``` #!/bin/bash DIR="/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=/dev/zero of=$DIR/$i/file$i bs=1M count=1 & 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 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 2. At the same time, we use the following perf command to capture IPC information: perf stat -e cycles,instructions -G test -a --repeat 5 -- sleep 10 1) Before applying this patchset: Performance counter stats for 'system wide' (5 runs): 454187219766 cycles test ( +- 1.84% ) 78896433101 instructions test # 0.17 insn per cycle ( +- 0.44% ) 10.0020430 +- 0.0000366 seconds time elapsed ( +- 0.00% ) 2) After applying this patchset: Performance counter stats for 'system wide' (5 runs): 841954709443 cycles test ( +- 15.80% ) (98.69%) 527258677936 instructions test # 0.63 insn per cycle ( +- 15.11% ) (98.68%) 10.01064 +- 0.00831 seconds time elapsed ( +- 0.08% ) We can see that IPC drops very seriously when calling down_read_trylock() at high frequency. After using SRCU, the IPC is at a normal level. Thanks, Qi > >