From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id D2A7D6B003D for ; Mon, 20 Apr 2009 21:40:46 -0400 (EDT) Received: from m2.gw.fujitsu.co.jp ([10.0.50.72]) by fgwmail5.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id n3L1fN8F029050 for (envelope-from kosaki.motohiro@jp.fujitsu.com); Tue, 21 Apr 2009 10:41:23 +0900 Received: from smail (m2 [127.0.0.1]) by outgoing.m2.gw.fujitsu.co.jp (Postfix) with ESMTP id DB43945DE62 for ; Tue, 21 Apr 2009 10:41:22 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (s2.gw.fujitsu.co.jp [10.0.50.92]) by m2.gw.fujitsu.co.jp (Postfix) with ESMTP id AC16345DD79 for ; Tue, 21 Apr 2009 10:41:22 +0900 (JST) Received: from s2.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id 89DCCE38008 for ; Tue, 21 Apr 2009 10:41:22 +0900 (JST) Received: from m106.s.css.fujitsu.com (m106.s.css.fujitsu.com [10.249.87.106]) by s2.gw.fujitsu.co.jp (Postfix) with ESMTP id D9A67E18001 for ; Tue, 21 Apr 2009 10:41:21 +0900 (JST) From: KOSAKI Motohiro Subject: Re: [PATCH V3] Fix Committed_AS underflow In-Reply-To: <1240256999.32604.330.camel@nimitz> References: <1240244120.32604.278.camel@nimitz> <1240256999.32604.330.camel@nimitz> Message-Id: <20090421102317.F113.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Date: Tue, 21 Apr 2009 10:41:20 +0900 (JST) Sender: owner-linux-mm@kvack.org To: Dave Hansen Cc: kosaki.motohiro@jp.fujitsu.com, Eric B Munson , linux-mm@kvack.org, linux-kernel@vger.kernel.org, mel@linux.vnet.ibm.com, cl@linux-foundation.org List-ID: > void vm_acct_memory(long pages) > { > long *local; > long local_min = -ACCT_THRESHOLD; > long local_max = ACCT_THRESHOLD; > long local_goal = 0; > > preempt_disable(); > local = &__get_cpu_var(committed_space); > *local += pages; > if (*local > local_max || *local < local_min) { > atomic_long_add(*local - local_goal, &vm_committed_space); > *local = local_goal; > } > preempt_enable(); > } > > But now consider if we changed the local_* variables a bit: > > long local_min = -(ACCT_THRESHOLD*2); > long local_max = 0 > long local_goal = -ACCT_THRESHOLD; > > We'll get some possibly *large* numbers in meminfo, but it will at least > never underflow. if *local == -(ACCT_THRESHOLD*2), *local - local_goal = -(ACCT_THRESHOLD*2) + ACCT_THRESHOLD = -ACCT_THRESHOLD Then, we still pass negative value to atomic_long_add(). IOW, vm_committed_space still can be negative value. Am I missing anything? -- 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