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[202.134.99.147]) by smtp.gmail.com with ESMTPSA id q65-20020a632a44000000b004efe1f24522sm3231075pgq.23.2023.02.21.06.21.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Feb 2023 06:21:49 -0800 (PST) Message-ID: <99bdfbec-2de4-b432-9649-09557d3f95d6@shopee.com> Date: Tue, 21 Feb 2023 22:21:45 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Re: [PATCH] mm/memcg: Skip high limit check in root memcg To: Michal Hocko Cc: hannes@cmpxchg.org, shakeelb@google.com, muchun.song@linux.dev, akpm@linux-foundation.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20230210094550.5125-1-haifeng.xu@shopee.com> <82918a12-d83e-10c0-0e04-eec26657b699@shopee.com> From: Haifeng Xu In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 956B7140008 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: txa93bupz36a96wj9rhb9trz8ymfgx4c X-HE-Tag: 1676989311-794482 X-HE-Meta: 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 eMAAB703 nqGVHdRJ/DXnXpw54jARNt9Z7uYxQsFYcJNvTQPGIa5+AirzBfCxp4be+LXrFP8NpNHFqdH0++ZZe2djQlkbNKz5EzPL6HRNgiSAbyjdz4nkGrGfWvcdlb+F8jmiXEAWiCPmEF38v42BEgXEdrlRGhhWbzXJLxtnxLEgIe1EehLq0RCW8nPvr9wQt6ESrSfT7SIglxFWLkVQrp7UKR9JjowUOowabWpbtyAY8byMiXO77Xno0rtgmJcewlMJJjKnqueEuY6swZHTteWxWEuZOytTpQA/cdDJsbFwK8sNOdLzplGGTAxfgWMBfVakifd3+Lf5I3SFUrbOFXNLlsJos6do8/L/CPAXrFa+AQgnrUjP1MhTG2R6mw50+Fcsb8cAEY7xbYnm9jKh4FFoP6BkOIwvHamy271q1LURAVKVy1tgdLEw= 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 2023/2/21 20:20, Michal Hocko wrote: > On Tue 21-02-23 18:29:39, Haifeng Xu wrote: >> >> >> On 2023/2/14 23:56, Michal Hocko wrote: >>> On Fri 10-02-23 09:45:50, Haifeng Xu wrote: >>>> The high limit checks the memory usage from given memcg to root memcg. >>>> However, there is no limit in root memcg. So this check makes no sense >>>> and we can ignore it. >>> >>> Is this check actually addining any benefit? Have you measured aby >>> performance gains by this change? >>> >>>> Signed-off-by: Haifeng Xu >>>> --- >>>> mm/memcontrol.c | 4 ++++ >>>> 1 file changed, 4 insertions(+) >>>> >>>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c >>>> index 73afff8062f9..a31a56598f29 100644 >>>> --- a/mm/memcontrol.c >>>> +++ b/mm/memcontrol.c >>>> @@ -2780,6 +2780,10 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask, >>>> do { >>>> bool mem_high, swap_high; >>>> >>>> + /* There is no need for root memcg to check high limit */ >>>> + if (mem_cgroup_is_root(memcg)) >>>> + break; >>>> + >>>> mem_high = page_counter_read(&memcg->memory) > >>>> READ_ONCE(memcg->memory.high); >>>> swap_high = page_counter_read(&memcg->swap) > >>>> -- >>>> 2.25.1 >>> >> >> test steps: >> 1. mkdir -p /sys/fs/cgroup/memory/test >> 2. echo $$ > /sys/fs/cgroup/memory/test/cgroup.procs >> 3. ./mmap_test >> >> The test result show that with or without the patch, the time taken is almost the same. > > This is in line with my expectation. So the question is whether the > additional check is really worth it. This patch doesn't bring any obvious benifit or harm, but the high limit check in root memcg seems a little weird. Maybe we can add this check？It all depends on your viewpoint. Thanks.