From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id 5DD856B0069 for ; Tue, 26 Sep 2017 05:15:01 -0400 (EDT) Received: by mail-pg0-f70.google.com with SMTP id p5so20824585pgn.7 for ; Tue, 26 Sep 2017 02:15:01 -0700 (PDT) Received: from szxga05-in.huawei.com (szxga05-in.huawei.com. [45.249.212.191]) by mx.google.com with ESMTPS id m73si5337733pfi.473.2017.09.26.02.14.59 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 26 Sep 2017 02:15:00 -0700 (PDT) Message-ID: <59CA1A57.5000905@huawei.com> Date: Tue, 26 Sep 2017 17:13:59 +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> <59CA125C.8000801@huawei.com> <20170926090255.jmocezs6s3lpd6p4@dhcp22.suse.cz> In-Reply-To: <20170926090255.jmocezs6s3lpd6p4@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 17:02, Michal Hocko wrote: > On Tue 26-09-17 16:39:56, Xishi Qiu wrote: >> 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? > > Any future page fault to the existing vma will result in the mlocked > page. That is what VM_LOCKED guarantess. > >> 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? > > This is still very fuzzy. What are you actually trying to achieve? I don't expect page fault any more after mlock. -- 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