From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f47.google.com (mail-pa0-f47.google.com [209.85.220.47]) by kanga.kvack.org (Postfix) with ESMTP id 1D9326B0038 for ; Thu, 19 Mar 2015 11:20:19 -0400 (EDT) Received: by pacwe9 with SMTP id we9so78506368pac.1 for ; Thu, 19 Mar 2015 08:20:18 -0700 (PDT) Received: from mail-pd0-x231.google.com (mail-pd0-x231.google.com. [2607:f8b0:400e:c02::231]) by mx.google.com with ESMTPS id ro12si3526447pab.108.2015.03.19.08.20.17 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 19 Mar 2015 08:20:18 -0700 (PDT) Received: by pdbni2 with SMTP id ni2so79154309pdb.1 for ; Thu, 19 Mar 2015 08:20:17 -0700 (PDT) Date: Thu, 19 Mar 2015 23:12:14 +0800 From: Wang YanQing Subject: Re: [RFC] Strange do_munmap in mmap_region Message-ID: <20150319151214.GA2175@udknight> References: <20150228064647.GA9550@udknight.ahead-top.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Konstantin Khlebnikov Cc: Mel Gorman , "linux-mm@kvack.org" , yinghai@kernel.org, Andrew Morton On Thu, Mar 19, 2015 at 11:33:41AM +0300, Konstantin Khlebnikov wrote: > On Sat, Feb 28, 2015 at 9:46 AM, Wang YanQing wrote: > > Hi Mel Gorman and all. > > > > I have read do_mmap_pgoff and mmap_region more than one hour, > > but still can't catch sense about below code in mmap_region: > > > > " > > /* Clear old maps */ > > error = -ENOMEM; > > munmap_back: > > if (find_vma_links(mm, addr, addr + len, &prev, &rb_link, &rb_parent)) { > > if (do_munmap(mm, addr, len)) > > return -ENOMEM; > > goto munmap_back; > > } > > " > > > > How can we just do_munmap overlapping vma without check its vm_flags > > and new vma's vm_flags? I must miss some important things, but I can't > > figure out. > > > > You give below comment about the code in "understand the linux memory manager":) > > > > " > > If a VMA was found and it is part of the new mmapping, this removes the > > old mmapping because the new one will cover both > > " > > > > But if new mmapping has different vm_flags or others' property, how > > can we just say the new one will cover both? > > > > I appreicate any clue and explanation about this headache question. > > > > Thanks. > > > > Mmap() creates new mapping in given range > (new vma might be merged to one or both of sides if possible) > so everything what was here before is unmapped in process. Not? Thanks for reply. Assme process has vma in region 4096-8192, one page size, mapped to a file's first 4096 bytes, then a new map want to create vma in range 0-8192 to map 4096-1288 in file, please tell me what's your meaning: "so everything what was here before is unmapped in process"? Why we can just delete old vma for first 4096 size in file which reside in range 4096-8192 without notify user process? And create the new vma to occupy range 0-8192, do you think "everything" is really the same? Process lost old map for file's first 4096 bytes, and we use a new map for 4096-1288 in file to lie it, and say "the same". Indeed, I have another question, I guess the answer could save me the same as this question. I have read get_unmapped_area, it seems it will return a unused enough region for new vma, and we hold mm->mmap_sem before vm_mmap_pgoff, why unused enough region return by get_unmapped_area has overlapping vma in mmap_region cause the first question? I have tested it, running system always call do_munmap in mmap_region, so I must miss something important, it is strange. Thanks again. > > > > > > > -- > > 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 -- 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