From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 3CB5E6B00C4 for ; Wed, 23 Nov 2011 02:50:11 -0500 (EST) Message-ID: <4ECCA578.6020700@cn.fujitsu.com> Date: Wed, 23 Nov 2011 15:49:12 +0800 From: Miao Xie Reply-To: miaox@cn.fujitsu.com MIME-Version: 1.0 Subject: Re: [patch for-3.2-rc3] cpusets: stall when updating mems_allowed for mempolicy or disjoint nodemask References: <4EC4C603.8050704@cn.fujitsu.com> <4EC62AEA.2030602@cn.fujitsu.com> <4ECC5FC8.9070500@cn.fujitsu.com> <4ECC7B1E.6020108@cn.fujitsu.com> In-Reply-To: Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Andrew Morton , Linus Torvalds , KOSAKI Motohiro , Paul Menage , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Tue, 22 Nov 2011 22:25:46 -0800 (pst), David Rientjes wrote: > On Wed, 23 Nov 2011, Miao Xie wrote: > >> This is a good idea. But I worry that oom will happen easily, because we do >> direct reclamation and compact by mems_allowed. >> > > Memory compaction actually iterates through each zone regardless of > whether it's allowed or not in the current context. Recall that the > nodemask passed into __alloc_pages_nodemask() is non-NULL only when there > is a mempolicy that restricts the allocations by MPOL_BIND. That nodemask > is not protected by get_mems_allowed(), so there's no change in > compaction's behavior with my patch. That nodemask is also protected by get_mems_allowed(). > Direct reclaim does, however, require mems_allowed staying constant > without the risk of early oom as you mentioned. It has its own > get_mems_allowed(), though, so it doesn't have the opportunity to change > until returning to the page allocator. It's possible that mems_allowed > will be different on the next call to get_pages_from_freelist() but we > don't know anything about that context: it's entirely possible that the > set of new mems has an abundance of free memory or are completely depleted > as well. So there's no strict need for consistency between the set of > allowed nodes during reclaim and the subsequent allocation attempt. All > we care about is that reclaim has a consistent set of allowed nodes to > determine whether it's making progress or not. > Agree. -- 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