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Fri, 19 Jul 2024 23:58:51 +0200 Message-ID: <54b7d944-37eb-4c3f-a994-13212aa3ed13@gmx.com> Date: Sat, 20 Jul 2024 07:28:45 +0930 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 1/3] memcontrol: define root_mem_cgroup for CONFIG_MEMCG=n cases To: Michal Hocko , 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 References: <2050f8a1bc181a9aaf01e0866e230e23216000f4.1721384771.git.wqu@suse.com> Content-Language: en-US From: Qu Wenruo Autocrypt: addr=quwenruo.btrfs@gmx.com; keydata= xsBNBFnVga8BCACyhFP3ExcTIuB73jDIBA/vSoYcTyysFQzPvez64TUSCv1SgXEByR7fju3o 8RfaWuHCnkkea5luuTZMqfgTXrun2dqNVYDNOV6RIVrc4YuG20yhC1epnV55fJCThqij0MRL 1NxPKXIlEdHvN0Kov3CtWA+R1iNN0RCeVun7rmOrrjBK573aWC5sgP7YsBOLK79H3tmUtz6b 9Imuj0ZyEsa76Xg9PX9Hn2myKj1hfWGS+5og9Va4hrwQC8ipjXik6NKR5GDV+hOZkktU81G5 gkQtGB9jOAYRs86QG/b7PtIlbd3+pppT0gaS+wvwMs8cuNG+Pu6KO1oC4jgdseFLu7NpABEB AAHNIlF1IFdlbnJ1byA8cXV3ZW5ydW8uYnRyZnNAZ214LmNvbT7CwJQEEwEIAD4CGwMFCwkI BwIGFQgJCgsCBBYCAwECHgECF4AWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCY00iVQUJDToH pgAKCRDCPZHzoSX+qNKACACkjDLzCvcFuDlgqCiS4ajHAo6twGra3uGgY2klo3S4JespWifr BLPPak74oOShqNZ8yWzB1Bkz1u93Ifx3c3H0r2vLWrImoP5eQdymVqMWmDAq+sV1Koyt8gXQ XPD2jQCrfR9nUuV1F3Z4Lgo+6I5LjuXBVEayFdz/VYK63+YLEAlSowCF72Lkz06TmaI0XMyj jgRNGM2MRgfxbprCcsgUypaDfmhY2nrhIzPUICURfp9t/65+/PLlV4nYs+DtSwPyNjkPX72+ LdyIdY+BqS8cZbPG5spCyJIlZonADojLDYQq4QnufARU51zyVjzTXMg5gAttDZwTH+8LbNI4 mm2YzsBNBFnVga8BCACqU+th4Esy/c8BnvliFAjAfpzhI1wH76FD1MJPmAhA3DnX5JDORcga CbPEwhLj1xlwTgpeT+QfDmGJ5B5BlrrQFZVE1fChEjiJvyiSAO4yQPkrPVYTI7Xj34FnscPj /IrRUUka68MlHxPtFnAHr25VIuOS41lmYKYNwPNLRz9Ik6DmeTG3WJO2BQRNvXA0pXrJH1fN GSsRb+pKEKHKtL1803x71zQxCwLh+zLP1iXHVM5j8gX9zqupigQR/Cel2XPS44zWcDW8r7B0 q1eW4Jrv0x19p4P923voqn+joIAostyNTUjCeSrUdKth9jcdlam9X2DziA/DHDFfS5eq4fEv ABEBAAHCwHwEGAEIACYCGwwWIQQt33LlpaVbqJ2qQuHCPZHzoSX+qAUCY00ibgUJDToHvwAK CRDCPZHzoSX+qK6vB/9yyZlsS+ijtsvwYDjGA2WhVhN07Xa5SBBvGCAycyGGzSMkOJcOtUUf tD+ADyrLbLuVSfRN1ke738UojphwkSFj4t9scG5A+U8GgOZtrlYOsY2+cG3R5vjoXUgXMP37 INfWh0KbJodf0G48xouesn08cbfUdlphSMXujCA8y5TcNyRuNv2q5Nizl8sKhUZzh4BascoK DChBuznBsucCTAGrwPgG4/ul6HnWE8DipMKvkV9ob1xJS2W4WJRPp6QdVrBWJ9cCdtpR6GbL iQi22uZXoSPv/0oUrGU+U5X4IvdnvT+8viPzszL5wXswJZfqfy8tmHM85yjObVdIG6AlnrrD In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:+rwUS6pqYSlruSzT3uI2slOzqyDeM7QHQ+J8pURnGMaSZ5Gz0ct FC5zpWqqOpXSe82Wu5LnUcHZxz1OwdDb/REVPCRE7oQtfWSRLwzkKpYFzNo7ZM3mrPbLPX+ eLYl0NkaSfUJzkyeXotBVxfwD5c00K4CNAj0zvqdqu6tz9z+2cehm6WWcKPALJW32d1d224 BP42f0OLwAW2qN8Ne1JfQ== X-Spam-Flag: NO UI-OutboundReport: notjunk:1;M01:P0:GLm5/WW0PR0=;k4TBVCug4O1/KN7+3QMogE2fpN4 NUsQ4XyPaBlLSJKYduISod1VJoBJzhKtn0rO0mVMKUeVZZuXgstfIG+OCpsanfcufvkwKUK0D 3TKFShSU74B/zEAXsTS4xwS+aNtmLTPfBoptTvX050jRlfhL1A1ImidqFAiJhLWK/zCby7hOk a1z7axN6OWNS9OCnRUGPoZ8P7RALstGs1m/MwcKDWsinzCNw2Fpd7Hg9ONXXEWK7yQPuLJJeA rfIcH3f5UwkmwPQ7Ec3bMgvPDMXjG3Ys+XsG3ygPX1McZYGST4wiXWltNSxwlDVXAg9MvBUF6 a1Cz3Ilwyy3dhfal6CrcMqDB+h5Tdnz3p16I3aVUnletYLE2QgVtVoXFtTPNNJ6wBz+3khFKu 9hT3cnIIB+fcMrWUYbgsVIdkvobTZy105vXYL8zf5zD7k63AIpC1tDHgJrw4EAyoNNuGS2v+q WnzKyqWJsYUe75OLCigZDVuiZkUmwunQ8p4z90bFUkWq9ZR2GvJjUcDOypxtc3cKZAY9FavdR uVciWuBP/cEXIPJ0Oj6pmm0oPy2J+wmi/cLIdOSA/KWZ70xOb7JhaZ14xBjyvis4mJ9qd1buX X43JblFqHCRC0AyAw3ObzNCuiKD/hEGilwGS3ZTDJHp9knsMc4FsKVCAo48MZ4wzqnfzgc85s P234k7P3cad6aJdP2kBF8Lz6N0gytUIEidTVpODcQTW3VGKL9CBd8whcoEH52f7lSUed4yENh je7V6lbN7vOgzGj/1e72so5FAJ1cNMY30V86PVFip2HW5l6UitK32RuKOutpIP3DO/p02bXSd dhnRCzErwjaROir78/5fC20w== =E5=9C=A8 2024/7/19 20:43, Michal Hocko =E5=86=99=E9=81=93: > 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=3Dn 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. > That can pass the compile, but waste the extra bytes for the pointer in the data section, even if no one is utilizing that pointer. Thanks, Qu