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Mon, 03 Mar 2025 10:49:36 -0800 (PST) Date: Mon, 3 Mar 2025 19:49:35 +0100 From: Michal =?utf-8?Q?Koutn=C3=BD?= To: Yosry Ahmed Cc: inwardvessel , tj@kernel.org, shakeel.butt@linux.dev, mhocko@kernel.org, hannes@cmpxchg.org, akpm@linux-foundation.org, linux-mm@kvack.org, cgroups@vger.kernel.org, kernel-team@meta.com Subject: Re: [PATCH 3/4 v2] cgroup: separate rstat locks for subsystems Message-ID: <6no5upfirmqnmyfz2vdbcuuxgnrfttvieznj6xjamvtpaz5ysv@swb4vfaqdmbh> References: <20250227215543.49928-1-inwardvessel@gmail.com> <20250227215543.49928-4-inwardvessel@gmail.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="obwbcojauwsjjxr6" Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 0BD0640006 X-Stat-Signature: uhnnw6j4gufrynksgynk4phbyghjruy4 X-HE-Tag: 1741027778-682347 X-HE-Meta: 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 d+zmupix K3ZYrBEQqs/CI755pi+PX6MOZaiKgnLccrNQrc9s/FLfGTlD4G2czorhmFR2WP9yJNcaomIGIQLlNOtPWr0p22F4yhCH08nzNgJMK8kDyJe+8k6PjGCRo8jx9rXpNt6V7/uneT9R1wgmooHrwqnftCuIQcmY18qd78vI+xh7mM3FstfapywegjXkEaKP4sbjCdIjJ5h1SX79JtKejdXRCil3/JL8VqGCUyHTuIXwVHULFr8966anL49PrlQIkuKMJAjTrxMMgvyNnKG1EqD4/ufoa/mrDFkUg1x+aaV50fPkwq7ig3AT+KBMXATunC2SirkCqNO50Dz0sef/RJepQmpJADW6X+uzG8ttugbgWOeoxHUjndBeJbk742SAyXVYXN1/ZF+9xJoE66joWg427J74pUjsxcdYRCmrBW7TdOhlP3id/eclUZ5alPg== 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: --obwbcojauwsjjxr6 Content-Type: text/plain; protected-headers=v1; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Subject: Re: [PATCH 3/4 v2] cgroup: separate rstat locks for subsystems MIME-Version: 1.0 On Mon, Mar 03, 2025 at 06:29:53PM +0000, Yosry Ahmed wrote: > I thought about this, but this would have unnecessary memory overhead as > we only need one lock per-subsystem. So having a lock in every single > css is wasteful. >=20 > Maybe we can put the lock in struct cgroup_subsys? Then we can still > initialize them in cgroup_init_subsys(). Ah, yes, muscle memory, of course I had struct cgroup_subsys\> in mind. > I think it will be confusing to have cgroup_rstat_boot() only initialize > some of the locks. >=20 > I think if we initialize the subsys locks in cgroup_init_subsys(), then > we should open code initializing the base locks in cgroup_init(), and > remove cgroup_rstat_boot(). Can this work? DEFINE_PER_CPU(raw_spinlock_t, cgroup_rstat_base_cpu_lock) =3D __RAW_SPIN_LOCK_INITIALIZER(cgroup_rstat_base_cpu_lock); (I see other places in kernel that assign into the per-cpu definition but I have no idea whether that does expands and links to what's expected. Neglecting the fact that the lock initializer is apparently not for external use.) > Alternatively, we can make cgroup_rstat_boot() take in a subsys and > initialize its lock. If we pass NULL, then it initialize the base locks. > In this case we can call cgroup_rstat_boot() for each subsystem that has > an rstat callback in cgroup_init() (or cgroup_init_subsys()), and then > once for the base locks. >=20 > WDYT? Such calls from cgroup_init_subsys() are fine too. --obwbcojauwsjjxr6 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQTd6mfF2PbEZnpdoAkt3Wney77BSQUCZ8X5vAAKCRAt3Wney77B SRgbAQDeQ7I2hYMnOwimwqQODn6GloN/rmgTR3tXGEK2Yw6SbQD9Hu0Vwnfv88pK 009vzj7AYz7SO3XUnhuNa1gMLTEd6QQ= =Twgp -----END PGP SIGNATURE----- --obwbcojauwsjjxr6--