From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with ESMTP id AE4A1900138 for ; Mon, 29 Aug 2011 03:57:56 -0400 (EDT) Date: Mon, 29 Aug 2011 09:57:31 +0200 From: Johannes Weiner Subject: Re: [patch 2/8] mm: memcg-aware global reclaim Message-ID: <20110829075731.GA32114@cmpxchg.org> References: <1306909519-7286-1-git-send-email-hannes@cmpxchg.org> <1306909519-7286-3-git-send-email-hannes@cmpxchg.org> <20110811210914.GB31229@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Ying Han Cc: KAMEZAWA Hiroyuki , Daisuke Nishimura , Michal Hocko , Andrew Morton , Rik van Riel , Minchan Kim , KOSAKI Motohiro , Mel Gorman , Greg Thelen , Michel Lespinasse , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hugh Dickins , Balbir Singh On Mon, Aug 29, 2011 at 12:22:02AM -0700, Ying Han wrote: > fix hierarchy_walk() to hold a reference to first mem_cgroup > > The first mem_cgroup returned from hierarchy_walk() is used to > terminate a round-trip. However there is no reference hold on > that which the first could be removed during the walking. The > patch including the following change: > > 1. hold a reference on the first mem_cgroup during the walk. > 2. rename the variable "root" to "target", which we found using > "root" is confusing in this content with root_mem_cgroup. better > naming is welcomed. Thanks for the report. This was actually not the only case that could lead to overlong (not necessarily endless) looping. With several scanning threads, a single thread may not encounter its first cgroup again for a long time, as the other threads would visit it. I changed this to use scan generations. Restarting the scan from id 0 starts the next scan generation. The iteration function returns NULL if the generation changed since a loop was started. This way, iterators can reliably detect whether they should call it quits without any requirements for previously encountered memcgs. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org