From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta8.messagelabs.com (mail6.bemta8.messagelabs.com [216.82.243.55]) by kanga.kvack.org (Postfix) with ESMTP id 5F4DC900138 for ; Thu, 8 Sep 2011 05:33:25 -0400 (EDT) Date: Thu, 8 Sep 2011 11:33:16 +0200 From: Johannes Weiner Subject: Re: [patch] mm: memcg: close race between charge and putback Message-ID: <20110908093316.GB1316@redhat.com> References: <1315467622-9520-1-git-send-email-jweiner@redhat.com> <20110908173042.4a6f8ac0.kamezawa.hiroyu@jp.fujitsu.com> <20110908085404.GA1316@redhat.com> <20110908181901.1d488d73.kamezawa.hiroyu@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110908181901.1d488d73.kamezawa.hiroyu@jp.fujitsu.com> Sender: owner-linux-mm@kvack.org List-ID: To: KAMEZAWA Hiroyuki Cc: Andrew Morton , Ying Han , Daisuke Nishimura , Balbir Singh , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu, Sep 08, 2011 at 06:19:01PM +0900, KAMEZAWA Hiroyuki wrote: > On Thu, 8 Sep 2011 10:54:04 +0200 > Johannes Weiner wrote: > > > On Thu, Sep 08, 2011 at 05:30:42PM +0900, KAMEZAWA Hiroyuki wrote: > > > On Thu, 8 Sep 2011 09:40:22 +0200 > > > Johannes Weiner wrote: > > > > > > > There is a potential race between a thread charging a page and another > > > > thread putting it back to the LRU list: > > > > > > > > charge: putback: > > > > SetPageCgroupUsed SetPageLRU > > > > PageLRU && add to memcg LRU PageCgroupUsed && add to memcg LRU > > > > > > > > > > I assumed that all pages are charged before added to LRU. > > > (i.e. event happens in charge->lru_lock->putback order.) > > > > > > But hmm, this assumption may be bad for maintainance. > > > Do you find a code which adds pages to LRU before charge ? > > > > > > Hmm, if there are codes which recharge the page to other memcg, > > > it will cause bug and my assumption may be harmful. > > > > Swap slots are read optimistically into swapcache and put to the LRU, > > then charged upon fault. > > Yes, then swap charge removes page from LRU before charge. > IIUC, it needed to do so because page->mem_cgroup may be replaced. But only from the memcg LRU. It's still on the global per-zone LRU, so reclaim could isolate/putback it during the charge. And then > > > > charge: putback: > > > > SetPageCgroupUsed SetPageLRU > > > > PageLRU && add to memcg LRU PageCgroupUsed && add to memcg LRU applies. And yes, it needs to fix up *pc->mem_cgroup's LRU statistics before the pointer get's overwritten. -- 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