From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id D2D0F6B0038 for ; Tue, 19 Dec 2017 10:12:22 -0500 (EST) Received: by mail-wr0-f199.google.com with SMTP id k44so5946672wre.1 for ; Tue, 19 Dec 2017 07:12:22 -0800 (PST) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id s26sor4529151wrb.64.2017.12.19.07.12.21 for (Google Transport Security); Tue, 19 Dec 2017 07:12:21 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <20171219124908.GS2787@dhcp22.suse.cz> References: <20171219000131.149170-1-shakeelb@google.com> <20171219124908.GS2787@dhcp22.suse.cz> From: Shakeel Butt Date: Tue, 19 Dec 2017 07:12:19 -0800 Message-ID: Subject: Re: [RFC PATCH] mm: memcontrol: memory+swap accounting for cgroup-v2 Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Tejun Heo , Li Zefan , Roman Gushchin , Vladimir Davydov , Greg Thelen , Johannes Weiner , Hugh Dickins , Andrew Morton , Linux MM , LKML , Cgroups , linux-doc@vger.kernel.org On Tue, Dec 19, 2017 at 4:49 AM, Michal Hocko wrote: > On Mon 18-12-17 16:01:31, Shakeel Butt wrote: >> The memory controller in cgroup v1 provides the memory+swap (memsw) >> interface to account to the combined usage of memory and swap of the >> jobs. The memsw interface allows the users to limit or view the >> consistent memory usage of their jobs irrespectibe of the presense of >> swap on the system (consistent OOM and memory reclaim behavior). The >> memory+swap accounting makes the job easier for centralized systems >> doing resource usage monitoring, prediction or anomaly detection. >> >> In cgroup v2, the 'memsw' interface was dropped and a new 'swap' >> interface has been introduced which allows to limit the actual usage of >> swap by the job. For the systems where swap is a limited resource, >> 'swap' interface can be used to fairly distribute the swap resource >> between different jobs. There is no easy way to limit the swap usage >> using the 'memsw' interface. >> >> However for the systems where the swap is cheap and can be increased >> dynamically (like remote swap and swap on zram), the 'memsw' interface >> is much more appropriate as it makes swap transparent to the jobs and >> gives consistent memory usage history to centralized monitoring systems. >> >> This patch adds memsw interface to cgroup v2 memory controller behind a >> mount option 'memsw'. The memsw interface is mutually exclusive with >> the existing swap interface. When 'memsw' is enabled, reading or writing >> to 'swap' interface files will return -ENOTSUPP and vice versa. Enabling >> or disabling memsw through remounting cgroup v2, will only be effective >> if there are no decendants of the root cgroup. >> >> When memsw accounting is enabled then "memory.high" is comapred with >> memory+swap usage. So, when the allocating job's memsw usage hits its >> high mark, the job will be throttled by triggering memory reclaim. > > From a quick look, this looks like a mess. The main motivation behind this patch is to convince that memsw has genuine use-cases. How to provide memsw is still in RFC stage. Suggestions and comments are welcomed. > We have agreed to go with > the current scheme for some good reasons. Yes I agree, when the swap is a limited resource the current 'swap' interface should be used to fairly distribute it between different jobs. > There are cons/pros for both > approaches but I am not convinced we should convolute the user API for > the usecase you describe. > Yes, there are pros & cons, therefore we should give users the option to select the API that is better suited for their use-cases and environment. Both approaches are not interchangeable. We use memsw internally for use-cases I mentioned in commit message. This is one of the main blockers for us to even consider cgroup-v2 for memory controller. >> Signed-off-by: Shakeel Butt -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org