From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx161.postini.com [74.125.245.161]) by kanga.kvack.org (Postfix) with SMTP id 514856B002B for ; Tue, 16 Oct 2012 14:56:56 -0400 (EDT) Date: Tue, 16 Oct 2012 14:55:42 -0400 From: Aristeu Rozanski Subject: Re: [PATCH v5 14/14] Add documentation about the kmem controller Message-ID: <20121016185542.GA5423@cathedrallabs.org> References: <1350382611-20579-1-git-send-email-glommer@parallels.com> <1350382611-20579-15-git-send-email-glommer@parallels.com> <0000013a6ad26c73-d043cf97-c44a-45c1-9cae-0a962e93a005-000000@email.amazonses.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <0000013a6ad26c73-d043cf97-c44a-45c1-9cae-0a962e93a005-000000@email.amazonses.com> Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: Glauber Costa , linux-mm@kvack.org, cgroups@vger.kernel.org, Mel Gorman , Tejun Heo , Andrew Morton , Michal Hocko , Johannes Weiner , kamezawa.hiroyu@jp.fujitsu.com, David Rientjes , Pekka Enberg , devel@openvz.org, linux-kernel@vger.kernel.org, Frederic Weisbecker , Pekka Enberg , Suleiman Souhlal On Tue, Oct 16, 2012 at 06:25:06PM +0000, Christoph Lameter wrote: > On Tue, 16 Oct 2012, Glauber Costa wrote: > > > > > + memory.kmem.limit_in_bytes # set/show hard limit for kernel memory > > + memory.kmem.usage_in_bytes # show current kernel memory allocation > > + memory.kmem.failcnt # show the number of kernel memory usage hits limits > > + memory.kmem.max_usage_in_bytes # show max kernel memory usage recorded > > Does it actually make sense to limit kernel memory? The user generally has > no idea how much kernel memory a process is using and kernel changes can > change the memory footprint. Given the fuzzy accounting in the kernel a > large cache refill (if someone configures the slab batch count to be > really big f.e.) can account a lot of memory to the wrong cgroup. The > allocation could fail. > > Limiting the total memory use of a process (U+K) would make more sense I > guess. Only U is probably sufficient? In what way would a limitation on > kernel memory in use be good? It's about preventing abuses caused by bugs or malicious use and avoiding groups stepping on each others' toes. You're saying that letting a group to allocate 32GB of paged memory is the same as 32GB of kernel memory? I don't belive sysadmins will keep a tight limit for kernel memory but rather a safety limit in case something goes wrong. usage_in_bytes will provide data to get the limits better adjusted. The innacuracy of the kmem accounting is (AFAIK) a cost tradeoff. -- Aristeu -- 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