From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH] fix bad behavior in use_hierarchy file Date: Mon, 25 Jun 2012 13:49:08 -0700 Message-ID: <20120625204908.GL3869@google.com> References: <1340616061-1955-1-git-send-email-glommer@parallels.com> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; bh=uO5rmuSBmM/XqX6+ZAuDW+Oa+SSI3+OAJPor8x5y3lg=; b=kaKDTQPLV4cofWj/d4rtl7O+osaca0Jib4860dmaPJ27NEM9iG5/iscL9q25jYOTZP DYKwwP1Nu8BNU8DOchayABZgiJk2RdSLUJHBmVTxB5+bC1VAoxAmSoQDQkS/30lf4k8t 1ydtTG9UNhZZ0fZWiMKUbEj5YnU4Q+5d/UrYpkU81TAeu8czomecNkWPkB3FDNDA5Ntc WT7ESrwSf7w5NA/jhJzmbSJQWw8/S7eBncQQ9eqP8tc0+Tri3pSqlvBCDvKazEYQBHXF gLUNRb/yUtd8jFuLynX1UvuCGTB0/bOQiWoJaV9uE1XDuaofY8r9AFh8UqcyGNOmKFJt aSnw== Content-Disposition: inline In-Reply-To: <1340616061-1955-1-git-send-email-glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Glauber Costa Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Andrew Morton , devel-GEFAQzZX7r8dnm+yROfE0A@public.gmane.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