From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753191Ab2E0U3J (ORCPT ); Sun, 27 May 2012 16:29:09 -0400 Received: from e28smtp05.in.ibm.com ([122.248.162.5]:46850 "EHLO e28smtp05.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752745Ab2E0U3H (ORCPT ); Sun, 27 May 2012 16:29:07 -0400 Date: Mon, 28 May 2012 01:58:48 +0530 From: "Aneesh Kumar K.V" To: David Rientjes Cc: linux-mm@kvack.org, mgorman@suse.de, KAMEZAWA Hiroyuki , dhillf@gmail.com, aarcange@redhat.com, mhocko@suse.cz, Andrew Morton , hannes@cmpxchg.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org Subject: Re: [PATCH -V6 07/14] memcg: Add HugeTLB extension Message-ID: <20120527202848.GC7631@skywalker.linux.vnet.ibm.com> References: <1334573091-18602-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1334573091-18602-8-git-send-email-aneesh.kumar@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) x-cbid: 12052720-8256-0000-0000-000002B2E3F9 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 24, 2012 at 02:52:26PM -0700, David Rientjes wrote: > On Mon, 16 Apr 2012, Aneesh Kumar K.V wrote: > > > This patch implements a memcg extension that allows us to control HugeTLB > > allocations via memory controller. The extension allows to limit the > > HugeTLB usage per control group and enforces the controller limit during > > page fault. Since HugeTLB doesn't support page reclaim, enforcing the limit > > at page fault time implies that, the application will get SIGBUS signal if it > > tries to access HugeTLB pages beyond its limit. This requires the application > > to know beforehand how much HugeTLB pages it would require for its use. > > > > The charge/uncharge calls will be added to HugeTLB code in later patch. > > Support for memcg removal will be added in later patches. > > > > Again, I disagree with this approach because it's adding the functionality > to memcg when it's unnecessary; it would be a complete legitimate usecase > to want to limit the number of globally available hugepages to a set of > tasks without incurring the per-page tracking from memcg. > > This can be implemented as a seperate cgroup and as we move to a single > hierarchy, you lose no functionality if you mount both cgroups from what > is done here. > > It would be much cleaner in terms of > > - build: not requiring ifdefs and dependencies on CONFIG_HUGETLB_PAGE, > which is a prerequisite for this functionality and is not for > CONFIG_CGROUP_MEM_RES_CTLR, I am not sure we have large number of #ifdef as you have outlined above. Most of the hugetlb limit code is well isolated already. If we were to split it as a seperate controller, we will be duplicating code related cgroup deletion, migration support etc from memcg, because in case of memcg and hugetlb limit they depend on struct page. So I would expect we would be end up #ifdef around that code or duplicate them in the new controller if we were to do hugetlb limit as a seperate controller. Another reason for it to be part of memcg is, it is normal to look at hugetlb usage also as a memory usage. One of the feedback I got for the earlier post is to see if i can enhace the current code to make sure memory.usage_in_bytes can also account for hugetlb usage. People would also like to look at memory.limit_in_bytes to limit total usage. (inclusive of hugetlb). > > - code: seperating hugetlb bits out from memcg bits to avoid growing > mm/memcontrol.c beyond its current 5650 lines, and > I can definitely look at spliting mm/memcontrol.c > - performance: not incurring any overhead of enabling memcg for per- > page tracking that is unnecessary if users only want to limit hugetlb > pages. > -aneesh