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[109.81.94.157]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3687868ba9asm1319052f8f.41.2024.07.19.04.13.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Jul 2024 04:13:41 -0700 (PDT) Date: Fri, 19 Jul 2024 13:13:40 +0200 From: Michal Hocko To: Qu Wenruo Cc: linux-btrfs@vger.kernel.org, hannes@cmpxchg.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, cgroups@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v7 1/3] memcontrol: define root_mem_cgroup for CONFIG_MEMCG=n cases Message-ID: References: <2050f8a1bc181a9aaf01e0866e230e23216000f4.1721384771.git.wqu@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2050f8a1bc181a9aaf01e0866e230e23216000f4.1721384771.git.wqu@suse.com> X-Stat-Signature: rb1zkzodxfb58myrbzorkmmiiq6kheis X-Rspamd-Queue-Id: 7839140005 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1721387623-961066 X-HE-Meta: U2FsdGVkX19hX6a6ATprll6vajA6Yvmw8z5+GmtcuYK7OCeTD+z4PAA3/rWEVYPqseqgyLsXf6jnir3E6NfLgzwc7EBysdPKUccds1JhMnoi9tjFj6lvXpAHXTy/FLQpAkgfmyQGx+vBbPGYgTDUxwKdT4utra1eX8j7PHCTUjVfdH1F/vU9eNVm3QZ2zH0wMyX6owHSM2BwOtT7NUgAic9UYZwEJ5A071Kl3Tr1c1Y42uOpWRaQxAzQ5+Wpn+sHyNK8OtnrJ0Qzw3YQ5eLTeS91OcO1geEN/godpYVbd1QfmzxMwriqmAIf2s6BWKcVLzHc5RHPRO3FCa6T39wSPBLCQF7JuViaEDjfmxCEjAWP2fHdkZvyYT+gxRCV8n1JBrQMXcNxt8IC4TvzJjqpeTTk5e2FJ0qtYI5iHVJ+i0hGCmhvM2UDi4ydZgriGEVp30E6EA78woDw151LehEVEJoIV+jHmiZUQ5MPiYzy7qt9olu7TJtR2MAZVJ9DfYFFSgfvT1DB/G+hupqmIGfdnwwjZ+HpdaZ+/MG3p4N031vtXPdW+WTEeyV5HNgaEH7f1/0R0uqcsL2iNEVi0/8XZCY2MO+xrLbJRgFa9lL6VxyvNoozfV61L0rosAFwM9cMcnGjjkKuQNIera44jT8lS8zJg46LRCUs56VAbS+GxO25Ubq8hmGnK+Z+VDLAiVr7K982nsrqodQgoLcsmR2pQ5j6MZFh3fS6Jk26AcKTlfV77HWmkQtWddFrnBbh9fulCjWd9UlNQRW1M7nZILNMrg7zP2JBdZEb62PK83YPQLZlsF/rokktfT2GbjdZSz1FXnE5pWTyviGrdEZ2xdsuvmQsPGOsRQbDJ/9LPJiIrV4UpCrpbIcWu6DMCZ6WvaFVN2+LAzZbAR12RklWJif/kWmBIr8JIeXQ/kKwFxT4LN7MXAGtO2cqWJVi6Lz32yR3WZyXVNNJLhgfflyYuzt Nvx5oiTc SQCEXl73wls2axwdTRUf7YbqWhUbJgjD4bIwFOsiBI8SiZKZ7x5yTkToy4xBWaCmsZ9wmYdqZwBNmQjKzBpRP0gJxahrRni2dj2eXfnHF0gjrdkrGQZgjj3cBd6CbXMF/Rwk2NtpapQodGZanSRd8NweSJgTKsd6O6MrpNKuLXxENa6DkdYHqJauQfzZo7w9MxYsdda6TfPw2t7mxaGIP0xhWeX2lHrH9SNPPvq4K396d7K5oL1PIj9STAiK7Zgmkn6K8A0+vWqbplWCgOHLLFZVLuEqmmEIc0j07zH+9BL+WZ1pIoT0KTbAdAkD0zPpUuhI87vCmaaIkDfQ= 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: List-Subscribe: List-Unsubscribe: On Fri 19-07-24 19:58:39, Qu Wenruo wrote: > There is an incoming btrfs patchset, which will use @root_mem_cgroup as > the active cgroup to attach metadata folios to its internal btree > inode, so that btrfs can skip the possibly costly charge for the > internal inode which is only accessible by btrfs itself. > > However @root_mem_cgroup is not always defined (not defined for > CONFIG_MEMCG=n case), thus all such callers need to do the extra > handling for different CONFIG_MEMCG settings. > > So here we add a special macro definition of root_mem_cgroup, making it > to always be NULL. Isn't just a declaration sufficient? Nothing should really dereference the pointer anyway. -- Michal Hocko SUSE Labs