From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vivek Goyal Subject: Re: [PATCH 2/2] cgroup: make css->refcnt clearing on cgroup removal optional Date: Sun, 1 Apr 2012 15:48:23 -0400 Message-ID: <20120401194823.GB6116@redhat.com> References: <20120330223423.GJ28934@google.com> <20120330223606.GK28934@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20120330223606.GK28934-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Tejun Heo Cc: ctalbott-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, rni-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, fweisbec-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Michal Hocko , Johannes Weiner , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On Fri, Mar 30, 2012 at 03:36:06PM -0700, Tejun Heo wrote: > Currently, cgroup removal tries to drain all css references. If there > are active css references, the removal logic waits and retries > ->pre_detroy() until either all refs drop to zero or removal is > cancelled. > > This semantics is unusual and adds non-trivial complexity to cgroup > core and IMHO is fundamentally misguided in that it couples internal > implementation details (references to internal data structure) with > externally visible operation (rmdir). To userland, this is a behavior > peculiarity which is unnecessary and difficult to expect (css refs is > otherwise invisible from userland), and, to policy implementations, > this is an unnecessary restriction (e.g. blkcg wants to hold css refs > for caching purposes but can't as that becomes visible as rmdir hang). Good to see this patch. Now annyoying rmdir hang with blkcg should be gone. Thanks Vivek From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753561Ab2DATtH (ORCPT ); Sun, 1 Apr 2012 15:49:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42450 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753206Ab2DATtF (ORCPT ); Sun, 1 Apr 2012 15:49:05 -0400 Date: Sun, 1 Apr 2012 15:48:23 -0400 From: Vivek Goyal To: Tejun Heo Cc: Li Zefan , containers@lists.linux-foundation.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, fweisbec@gmail.com, rni@google.com, ctalbott@google.com, Johannes Weiner , Michal Hocko , Balbir Singh , KAMEZAWA Hiroyuki Subject: Re: [PATCH 2/2] cgroup: make css->refcnt clearing on cgroup removal optional Message-ID: <20120401194823.GB6116@redhat.com> References: <20120330223423.GJ28934@google.com> <20120330223606.GK28934@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120330223606.GK28934@google.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Mar 30, 2012 at 03:36:06PM -0700, Tejun Heo wrote: > Currently, cgroup removal tries to drain all css references. If there > are active css references, the removal logic waits and retries > ->pre_detroy() until either all refs drop to zero or removal is > cancelled. > > This semantics is unusual and adds non-trivial complexity to cgroup > core and IMHO is fundamentally misguided in that it couples internal > implementation details (references to internal data structure) with > externally visible operation (rmdir). To userland, this is a behavior > peculiarity which is unnecessary and difficult to expect (css refs is > otherwise invisible from userland), and, to policy implementations, > this is an unnecessary restriction (e.g. blkcg wants to hold css refs > for caching purposes but can't as that becomes visible as rmdir hang). Good to see this patch. Now annyoying rmdir hang with blkcg should be gone. Thanks Vivek