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Wed, 19 Mar 2025 11:06:47 -0700 (PDT) Date: Wed, 19 Mar 2025 14:06:43 -0400 From: Johannes Weiner To: Yosry Ahmed Cc: Greg Thelen , Tejun Heo , Michal =?iso-8859-1?Q?Koutn=FD?= , Andrew Morton , Eric Dumazet , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Eric Dumazet Subject: Re: [PATCH] cgroup/rstat: avoid disabling irqs for O(num_cpu) Message-ID: <20250319180643.GC1876369@cmpxchg.org> References: <20250319071330.898763-1-gthelen@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspam-User: X-Rspamd-Queue-Id: 1B5D440017 X-Rspamd-Server: rspam05 X-Stat-Signature: s8uqwhr348kuq5a9ecibn31ssz5w4rmx X-HE-Tag: 1742407608-993191 X-HE-Meta: U2FsdGVkX18PwPz6coHc+dFBuzm3xhUNK+uP31n7zDlRVwmrOXANC7ruk9Ojvd/ObaGM3WZNwFRAvbmDcMDQbkBVOf8APqPxweJiTU4Sb7EAmFBaBIIlTKMzTSzWUS0AgONLSkaYffBWw3HQZzDT2ei+ZWKgZkYEznoBQGBg8F08O/JPvazOMhqMHQ30ANjvR8aBdAtoFeGV3tkjKkaC24r7F0kQpge4qoFYVOVPqQb9Ab53lHWsCgueR6ydspxsn4LVoRp8Cwaqu4x69R9fl85V6byL9RN6UiLdsff/XY76cVxCwbq/EfRUfwvW2sOl9UTj95BG55oZFuSO5XqVTYGnsuzCJcfz2zd62LNOy/60gZTr/xEAIX4NkJBGx0xuk6r8GwFR64jnPguqwvrcfiQezOftX850WKinVRtNIlzJ7oER0sXkCq2E51XSjeIJjebC8V/5/ad/etAVIRz9n8DEdyTRYtkM9HIdk7b3Awl3JPmueo8rnoG9cU57TYpNL+knb91cQ4rwvUwj6DJxrGdUUYiNSy9F64vB5Ky4qzAgIZvjlQOLwHLDK84dHQCLozu1ztsAMGOAr3GN8k1BlK5QtNHuPwLNiZ5HS/92BBd0DvDtPT7fc3NDiOpf+Dt8xKE1Y5S/7jvbIrZ/bDqBYjQHzFpNgxV40MHzLAmvgu2TbFGozNVsDeu/bUElVw+Zgz0i9jFADslbGHEovOaB3AJrsPH+7SZ0g1xxPHgcKdgtNFXXmNaczCaN0S31glVl+A5y5G4FSqAf8lyTHFBA0y9pd02Fzax5hyC5M8iFvOX67gARofP23BLfCmqytubfhLENKRj9VR9z6ANpdfvIKZM5O8LKd4sMHCsEqTb3qHmyEkZ9TnpaEkUky8JDRL9omj+xgFR/tqjgE6th3LA2DaTEaFWfhz4jJzsD60S3TxJbcFwfibd5GjBhAJxEseJRlCOuSi6Zsb41ifrvEIx tnm+yrZs 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 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 Wed, Mar 19, 2025 at 05:16:02PM +0000, Yosry Ahmed wrote: > @@ -365,9 +352,8 @@ __bpf_kfunc void cgroup_rstat_flush(struct cgroup *cgrp) > void cgroup_rstat_flush_hold(struct cgroup *cgrp) > __acquires(&cgroup_rstat_lock) > { > - might_sleep(); > + cgroup_rstat_flush(cgrp); > __cgroup_rstat_lock(cgrp, -1); > - cgroup_rstat_flush_locked(cgrp); > } Might as well remove cgroup_rstat_flush_hold/release entirely? There are no external users, and the concept seems moot when the lock is dropped per default. cgroup_base_stat_cputime_show() can open-code the lock/unlock to stabilize the counts while reading. (btw, why do we not have any locking around the root stats in cgroup_base_stat_cputime_show()? There isn't anything preventing a reader from seeing all zeroes if another reader runs the memset() on cgrp->bstat, is there? Or double times...)