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Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.9.1 Subject: Re: [PATCH] mm: compaction: optimize compact_memory to comply with the admin-guide From: Wen Yang To: Andrew Morton Cc: Mel Gorman , Oscar Salvador , William Lam , Fu Wei , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20230411134801.a4aadef5aba0f51e0d44bb7a@linux-foundation.org> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 387E340011 X-Stat-Signature: skk5r8rfgjoi39zx5iw5hs6616x9oqpn X-HE-Tag: 1681580580-224396 X-HE-Meta: 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 8IgupkLK gWX3mSD382wAJEoDlmwIDxZGHPGzYDSXJaZyEG5HMJKwi7gdUoKxLbGk0u7DGAKZmOa5hYwDehdA8XDRMbazwCObDGcg6VaFL4qKy0jfCTcbQmM5f8bN+B4ON8I68U+AKDfvNkXJzF/6B8VeCZ5B5TgpK9VR2XOvsu9RwkLIj+n3mtOiPnyLcYVzvk18WBsdmQtz+UkC9L77zPlwwgPk6efFC3cWsZ1G8Xv7iuHHUiJJy+n0lEssSsWcMINxfTLMKKBXf+LTTCfYn9E0mXLL0ZRed6OD05Klx0SAk9y3vTk3ygS2xGYKJbaaz/X+l6MWlVGqef4T7BPv6cB/DiPR+BIBJwujj+JZa+gwB+wkgwfKUtQd1ruPcC2ics1MN4kBNtXj5x9qmI++7XL6mKehWth5qag== X-Bogosity: Ham, tests=bogofilter, spamicity=0.064849, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 在 2023/4/13 00:54, Wen Yang 写道: > > 在 2023/4/12 04:48, Andrew Morton 写道: >> On Wed, 12 Apr 2023 02:24:26 +0800 wenyang.linux@foxmail.com wrote: >> >>> For the /proc/sys/vm/compact_memory file, the admin-guide states: >>> When 1 is written to the file, all zones are compacted such that free >>> memory is available in contiguous blocks where possible. This can be >>> important for example in the allocation of huge pages although >>> processes >>> will also directly compact memory as required >>> >>> But it was not strictly followed, writing any value would cause all >>> zones to be compacted. In some critical scenarios, some applications >>> operating it, such as echo 0, have caused serious problems. >> Really?  You mean someone actually did this and didn't observe the >> effect during their testing? > > Thanks for your reply. > > Since /proc/sys/vm/compact_memory has been well documented for over a > decade: > > https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/Documentation/admin-guide/sysctl/vm.rst#n109 > > > it is believed that only writing 1 will trigger trigger all zones to > be compacted. > > Especially for those who write applications, they may only focus on > documentation and generally do not read kernel code.  Moreover, such > problems are not easily detected through testing on low pressure > machines. > > Writing any meaningful or meaningless values will trigger it and > affect the entire server: > > # echo 1 > /proc/sys/vm/compact_memory > # echo 0 > /proc/sys/vm/compact_memory > # echo dead > /proc/sys/vm/compact_memory > # echo "hello world" > /proc/sys/vm/compact_memory > > The implementation of this high-risk operation may require following > the admin-guides. > > -- > > Best wishes, > > Wen > > Hello, do you think it's better to optimize the sysctl_compaction_handler code or update the admin-guide document? -- Best wishes, Wen >>> It has been slightly optimized to comply with the admin-guide. >