From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Weiner Subject: Re: [RFC PATCH 0/2] mm/memcontrol: Finer-grained memory control Date: Thu, 11 Apr 2019 11:31:13 -0400 Message-ID: <20190411153113.GA32469@cmpxchg.org> References: <20190410191321.9527-1-longman@redhat.com> <20190410195443.GL10383@dhcp22.suse.cz> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=3iJKixxuhPHlPoZGh40Oi3FjBSMfJGKskcYDOhWiKGQ=; b=1hwtmF+hHKwJ6ukgkNYfDzhggthKX24NSk2lZP6PHZKK0OuNX/iwCbFuFzPm57tK2P gdNbZDktsfSgeGeQ08V+cWQQmM0Jw9isIS3WhHhuBTBJs2BToG6Tb/eO7VtZT59u6C0V aMA/z6Z3nDieLbf8Pn1TG/Xw4o+Td3G5OUt8msHHo+q/xNxiOR6PHHQXP5i2DL22SxZS yH7x9QB6XSulVn4JbEd2bqKkJKiFN4KVm9Z7DnJO4wXcwe1DtLf+7FHHDf3aOuEHrf0U NlNYSwvNKgcrNkisAliIuUeCvEh/7u7of22dG3702V13GJKwj6q5D4lfNuB0qJuxBKmm 70SA== Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Waiman Long Cc: Michal Hocko , Tejun Heo , Li Zefan , Jonathan Corbet , Vladimir Davydov , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-doc@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Roman Gushchin , Shakeel Butt , Kirill Tkhai , Aaron Lu On Thu, Apr 11, 2019 at 10:02:16AM -0400, Waiman Long wrote: > On 04/10/2019 03:54 PM, Michal Hocko wrote: > > On Wed 10-04-19 15:13:19, Waiman Long wrote: > >> The current control mechanism for memory cgroup v2 lumps all the memory > >> together irrespective of the type of memory objects. However, there > >> are cases where users may have more concern about one type of memory > >> usage than the others. > >> > >> We have customer request to limit memory consumption on anonymous memory > >> only as they said the feature was available in other OSes like Solaris. > > Please be more specific about a usecase. > > From that customer's point of view, page cache is more like common goods > that can typically be shared by a number of different groups. Depending > on which groups touch the pages first, it is possible that most of those > pages can be disproportionately attributed to one group than the others. > > Anonymous memory, on the other hand, are not shared and so can more > correctly represent the memory footprint of an application. Of course, > there are certainly cases where an application can have large private > files that can consume a lot of cache pages. These are probably not the > case for the applications used by that customer. I don't understand what the goal is. What do you accomplish by only restricting anon memory? Are you trying to contain malfunctioning applications? Malicious applications? Cache can apply as much pressure to the system as anon can. So if you are in the position to ask your applications to behave wrt cache, surely you can ask them to behave wrt anon as well...? This also answers only one narrow question out of the many that arise when heavily sharing cache. The accounting isn't done right, memory.current of the participating cgroups will make no sense, IO read and writeback burden is assigned to random cgroups. > >> For simplicity, the limit is not hierarchical and applies to only tasks > >> in the local memory cgroup. > > This is a no-go to begin with. > > The reason for doing that is to introduce as little overhead as > possible. We can certainly make it hierarchical, but it will complicate > the code and increase runtime overhead. Another alternative is to limit > this feature to only leaf memory cgroups. That should be enough to cover > what the customer is asking for and leave room for future hierarchical > extension, if needed. I agree with Michal, this is a no-go. It involves userspace ABI that we have to maintain indefinitely, so it needs to integrate properly with the overall model of the cgroup2 interface. That includes hierarchical support, but as per above it includes wider questions of how this is supposed to integrate with the concepts of comprehensive resource control. How it integrates with the accounting (if you want to support shared pages, they should also be accounted as shared and not to random groups), the relationships with connected resources such as IO (in a virtual memory system that can do paging, memory and IO are fungible, so if you want to be able to share one, you have to be able to share the other as well to the same extent), how it integrates with memory.low protection etc. As it stands, I don't see this patch set addressing any of these.