From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030439AbdIZIkM (ORCPT ); Tue, 26 Sep 2017 04:40:12 -0400 Received: from szxga04-in.huawei.com ([45.249.212.190]:7001 "EHLO szxga04-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030426AbdIZIkJ (ORCPT ); Tue, 26 Sep 2017 04:40:09 -0400 Message-ID: <59CA125C.8000801@huawei.com> Date: Tue, 26 Sep 2017 16:39:56 +0800 From: Xishi Qiu User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:12.0) Gecko/20120428 Thunderbird/12.0.1 MIME-Version: 1.0 To: Michal Hocko CC: Joonsoo Kim , Vlastimil Babka , Mel Gorman , Linux MM , LKML , zhong jiang , yeyunfeng , , "Zhoukang (A)" Subject: Re: [RFC] a question about mlockall() and mprotect() References: <59CA0847.8000508@huawei.com> <20170926081716.xo375arjoyu5ytcb@dhcp22.suse.cz> In-Reply-To: <20170926081716.xo375arjoyu5ytcb@dhcp22.suse.cz> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.25.179] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A020201.59CA1267.00F9,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2014-11-16 11:51:01, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 432574f07201fb2747e3a3451780104b Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017/9/26 16:17, Michal Hocko wrote: > On Tue 26-09-17 15:56:55, Xishi Qiu wrote: >> When we call mlockall(), we will add VM_LOCKED to the vma, >> if the vma prot is ---p, > > not sure what you mean here. apply_mlockall_flags will set the flag on > all vmas except for special mappings (mlock_fixup). This phase will > cause that memory reclaim will not free already mapped pages in those > vmas (see page_check_references and the lazy mlock pages move to > unevictable LRUs). > >> then mm_populate -> get_user_pages will not alloc memory. > > mm_populate all the vmas with pages. Well there are certainly some > constrains - e.g. memory cgroup hard limit might be hit and so the > faulting might fail. > >> I find it said "ignore errors" in mm_populate() >> static inline void mm_populate(unsigned long addr, unsigned long len) >> { >> /* Ignore errors */ >> (void) __mm_populate(addr, len, 1); >> } > > But we do not report the failure because any failure past > apply_mlockall_flags would be tricky to handle. We have already dropped > the mmap_sem lock so some other address space operations could have > interfered. > >> And later we call mprotect() to change the prot, then it is >> still not alloc memory for the mlocked vma. >> >> My question is that, shall we alloc memory if the prot changed, >> and who(kernel, glibc, user) should alloc the memory? > > I do not understand your question but if you are asking how to get pages > to map your vmas then touching that area will fault the memory in. Hi Michal, syscall mlockall() will first apply the VM_LOCKED to the vma, then call mm_populate() to map the vmas. mm_populate populate_vma_page_range __get_user_pages check_vma_flags And the above path maybe return -EFAULT in some case, right? If we call mprotect() to change the prot of vma, just let check_vma_flags() return 0, then we will get the mlocked pages in following page-fault, right? My question is that, shall we map the vmas immediately when the prot changed? If we should map it immediately, who(kernel, glibc, user) do this step? Thanks, Xishi Qiu