From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [RFC PATCH] memcg: use root_mem_cgroup when css is inherited Date: Wed, 24 Aug 2022 12:27:00 +0200 Message-ID: References: Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1661336821; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=svip1HnOF9D7Fl9aKofEvyk0pEgENUVlEuB1mZtboTA=; b=BSwbM9o5a63Dsl3aydVUid7PDlzXWhAjXTXwpvHPRto/Y+Z4jx+DSo3SpxBtt/QERnMVCr Bsy6tdYVt8qrRFwuly1qta1c5/YJ/QwiiPW6MwVlDOnVjadS+2kc3loarhh3eYS9c9OEfd Ry2BcmegFWJQ3RRPza792trSufbhx4o= Content-Disposition: inline In-Reply-To: List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Zhaoyang Huang Cc: Suren Baghdasaryan , Tejun Heo , Shakeel Butt , "zhaoyang.huang" , Johannes Weiner , Linux MM , LKML , Cgroups , Ke Wang , Zefan Li , Roman Gushchin , Muchun Song On Wed 24-08-22 17:34:42, Zhaoyang Huang wrote: > On Wed, Aug 24, 2022 at 3:50 PM Michal Hocko wrote: > > > > On Wed 24-08-22 10:23:14, Zhaoyang Huang wrote: > > > On Tue, Aug 23, 2022 at 7:51 PM Michal Hocko wrote: > > [...] > > > > One way to achieve that would be shaping the hierarchy the following way > > > > root > > > > / \ > > > > no_memcg[1] memcg[2] > > > > |||||||| ||||| > > > > app_cgroups app_cgroups > > > > > > > > with > > > > no_memcg.subtree_control = "" > > > > memcg.subtree_control = memory > > > > > > > > no? > > > According to my understanding, No as there will be no no_memcg. All > > > children groups under root would have its cgroup.controllers = memory > > > as long as root has memory enabled. > > > > Correct > > > > > Under this circumstance, all > > > descendants group under 'no_memcg' will charge memory to its parent > > > group. > > > > Correct. And why is that a problem? I thought you main concern was a per > > application LRUs. With the above configuration all app_cgroups which do > > not require an explicit memory control will share the same (no_memcg) > > LRU and they will be aged together. > I can't agree since this indicates the processes want memory free > depending on a specific hierarchy which could have been determined by > other subsys. I really fail to understand your requirements. > IMHO, charging the pages which out of explicitly memory > enabled group to root could solve all of the above constraints with no > harm. This would break the hierarchical property of the controller. So a strong no no. Consider the following example root | A controllers="memory" memory.max = 1G subtree_control="" | | | A1 A2 A3 althought A1,2,3 do not have their memory controller enabled explicitly they are still constrained by the A memcg limit. If you just charge to the root because it doesn't have memory controller enabled explicitly then you just evade that constrain. I hope you understand why that is a problem. -- Michal Hocko SUSE Labs