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Tue, 30 Aug 2022 07:12:49 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id 8VW6F3G4DWNXLwAAMHmgww (envelope-from ); Tue, 30 Aug 2022 07:12:49 +0000 Date: Tue, 30 Aug 2022 09:12:48 +0200 From: Michal Hocko To: Kairui Song Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, Johannes Weiner , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm: memcontrol: remove mem_cgroup_kmem_disabled Message-ID: References: <20220830055949.12640-1-ryncsn@gmail.com> <20220830055949.12640-2-ryncsn@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1661843570; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; 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spf=pass (imf31.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.28 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com X-Rspamd-Server: rspam08 X-HE-Tag: 1661843570-491751 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: On Tue 30-08-22 15:06:57, Kairui Song wrote: > Michal Hocko 于2022年8月30日周二 14:45写道： > > > > On Tue 30-08-22 13:59:48, Kairui Song wrote: > > > From: Kairui Song > > > > > > There are currently two helpers for checking if cgroup kmem > > > accounting is enabled: > > > > > > - mem_cgroup_kmem_disabled > > > - memcg_kmem_enabled > > > > Yes, this is a bit confusing indeed! > > > > > mem_cgroup_kmem_disabled is a simple helper that returns true if > > > cgroup.memory=nokmem is specified, otherwise returns false. > > > > > > memcg_kmem_enabled is a bit different, it returns true if > > > cgroup.memory=nokmem is not specified and there is at least one > > > non-root cgroup ever created. And once there is any non-root memcg > > > created, it won't go back to return false again. > > > > > > This may help improve performance for some corner use cases where > > > the user enables memory cgroup and kmem accounting globally but never > > > create any cgroup. > > > > > > Considering that corner case is rare, especially nowadays cgroup is > > > widely used as a standard way to organize services. > > > > Is it really that rare? Most configurations would use a default setup, so > > both MEMCG enabled and without nokmem on cmd line yet the memory > > controller is not enabled in their setups. > > Actually I don't have too much confidence saying that as well... but > AFAIK, almost all distros will create a few sub cgroup on boot by the > init (eg. openrc, finit, systemd). Yeah, but do they enable the memory controller as well? Unless I am missing something this will require at least one memcg enabled cgroup to be created. -- Michal Hocko SUSE Labs