From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932793AbcG1H7L (ORCPT ); Thu, 28 Jul 2016 03:59:11 -0400 Received: from mail-wm0-f51.google.com ([74.125.82.51]:36364 "EHLO mail-wm0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932773AbcG1H66 (ORCPT ); Thu, 28 Jul 2016 03:58:58 -0400 Date: Thu, 28 Jul 2016 09:58:56 +0200 From: Michal Hocko To: Xishi Qiu Cc: Tejun Heo , Ingo Molnar , Peter Zijlstra , LKML , Linux MM , Andy Lutomirski , Yisheng Xie Subject: Re: [RFC] can we use vmalloc to alloc thread stack if compaction failed Message-ID: <20160728075856.GE31860@dhcp22.suse.cz> References: <5799AF6A.2070507@huawei.com> <20160728072028.GC31860@dhcp22.suse.cz> <5799B741.8090506@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5799B741.8090506@huawei.com> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 28-07-16 15:41:53, Xishi Qiu wrote: > On 2016/7/28 15:20, Michal Hocko wrote: > > > On Thu 28-07-16 15:08:26, Xishi Qiu wrote: > >> Usually THREAD_SIZE_ORDER is 2, it means we need to alloc 16kb continuous > >> physical memory during fork a new process. > >> > >> If the system's memory is very small, especially the smart phone, maybe there > >> is only 1G memory. So the free memory is very small and compaction is not > >> always success in slowpath(__alloc_pages_slowpath), then alloc thread stack > >> may be failed for memory fragment. > > > > Well, with the current implementation of the page allocator those > > requests will not fail in most cases. The oom killer would be invoked in > > order to free up some memory. > > > > Hi Michal, > > Yes, it success in most cases, but I did have seen this problem in some > stress-test. > > DMA free:470628kB, but alloc 2 order block failed during fork a new process. > There are so many memory fragments and the large block may be soon taken by > others after compact because of stress-test. > > --- dmesg messages --- > 07-13 08:41:51.341 <4>[309805.658142s][pid:1361,cpu5,sManagerService]sManagerService: page allocation failure: order:2, mode:0x2000d1 Yes but this is __GFP_DMA allocation. I guess you have already reported this failure and you've been told that this is quite unexpected for the kernel stack allocation. It is your out-of-tree patch which just makes things worse because DMA restricted allocations are considered "lowmem" and so they do not invoke OOM killer and do not retry like regular GFP_KERNEL allocations. -- Michal Hocko SUSE Labs