From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx105.postini.com [74.125.245.105]) by kanga.kvack.org (Postfix) with SMTP id 3F8376B038F for ; Mon, 25 Jun 2012 16:49:13 -0400 (EDT) Received: by pbbrp2 with SMTP id rp2so8775046pbb.14 for ; Mon, 25 Jun 2012 13:49:12 -0700 (PDT) Date: Mon, 25 Jun 2012 13:49:08 -0700 From: Tejun Heo Subject: Re: [PATCH] fix bad behavior in use_hierarchy file Message-ID: <20120625204908.GL3869@google.com> References: <1340616061-1955-1-git-send-email-glommer@parallels.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1340616061-1955-1-git-send-email-glommer@parallels.com> Sender: owner-linux-mm@kvack.org List-ID: To: Glauber Costa Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , devel@openvz.org, Dhaval Giani , Michal Hocko , Kamezawa Hiroyuki , Johannes Weiner On Mon, Jun 25, 2012 at 01:21:01PM +0400, Glauber Costa wrote: > I have an application that does the following: > > * copy the state of all controllers attached to a hierarchy > * replicate it as a child of the current level. > > I would expect writes to the files to mostly succeed, since they > are inheriting sane values from parents. > > But that is not the case for use_hierarchy. If it is set to 0, we > succeed ok. If we're set to 1, the value of the file is automatically > set to 1 in the children, but if userspace tries to write the > very same 1, it will fail. That same situation happens if we > set use_hierarchy, create a child, and then try to write 1 again. > > Now, there is no reason whatsoever for failing to write a value > that is already there. It doesn't even match the comments, that > states: > > /* If parent's use_hierarchy is set, we can't make any modifications > * in the child subtrees... > > since we are not changing anything. > > The following patch tests the new value against the one we're storing, > and automatically return 0 if we're not proposing a change. A bit of delta but is there any chance we can either deprecate .use_hierarhcy or at least make it global toggle instead of subtree thing? This seems needlessly complicated. :( -- tejun -- 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