From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f71.google.com (mail-oi0-f71.google.com [209.85.218.71]) by kanga.kvack.org (Postfix) with ESMTP id 0254C6B0038 for ; Tue, 26 Sep 2017 04:43:24 -0400 (EDT) Received: by mail-oi0-f71.google.com with SMTP id a74so11906410oib.7 for ; Tue, 26 Sep 2017 01:43:23 -0700 (PDT) Received: from szxga04-in.huawei.com (szxga04-in.huawei.com. [45.249.212.190]) by mx.google.com with ESMTPS id r42si510878ote.489.2017.09.26.01.43.22 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 26 Sep 2017 01:43:23 -0700 (PDT) Message-ID: <59CA125C.8000801@huawei.com> Date: Tue, 26 Sep 2017 16:39:56 +0800 From: Xishi Qiu MIME-Version: 1.0 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 Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Joonsoo Kim , Vlastimil Babka , Mel Gorman , Linux MM , LKML , zhong jiang , yeyunfeng , wanghaitao12@huawei.com, "Zhoukang (A)" 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 -- 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