From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id F0BEA6B025F for ; Thu, 28 Jul 2016 05:31:45 -0400 (EDT) Received: by mail-pf0-f197.google.com with SMTP id o124so45689698pfg.1 for ; Thu, 28 Jul 2016 02:31:45 -0700 (PDT) Received: from szxga03-in.huawei.com (szxga03-in.huawei.com. [119.145.14.66]) by mx.google.com with ESMTPS id v88si11603027pfj.110.2016.07.28.02.31.44 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 28 Jul 2016 02:31:45 -0700 (PDT) Message-ID: <5799C612.1050502@huawei.com> Date: Thu, 28 Jul 2016 16:45:06 +0800 From: Xishi Qiu MIME-Version: 1.0 Subject: Re: [RFC] can we use vmalloc to alloc thread stack if compaction failed References: <5799AF6A.2070507@huawei.com> <20160728072028.GC31860@dhcp22.suse.cz> <5799B741.8090506@huawei.com> <20160728075856.GE31860@dhcp22.suse.cz> In-Reply-To: <20160728075856.GE31860@dhcp22.suse.cz> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Tejun Heo , Ingo Molnar , Peter Zijlstra , LKML , Linux MM , Andy Lutomirski , Yisheng Xie On 2016/7/28 15:58, Michal Hocko wrote: > 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. Hi Michal, Yes, we add GFP_DMA, but I don't think this is the key for the problem. If we do oom-killer, maybe we will get a large block later, but there is enough free memory before oom(although most of them are fragments). I wonder if we can alloc success without kill any process in this situation. Maybe use vmalloc is a good way, but I don't know the influence. Thanks, Xishi Qiu -- 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