From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754637AbbBKWJS (ORCPT ); Wed, 11 Feb 2015 17:09:18 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:42658 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753834AbbBKWJR (ORCPT ); Wed, 11 Feb 2015 17:09:17 -0500 Date: Wed, 11 Feb 2015 14:09:15 -0800 From: Andrew Morton To: Naoya Horiguchi Cc: Shiraz Hashim , "linux-mm@kvack.org" , "oleg@redhat.com" , "gorcunov@openvz.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 1/1] mm: pagemap: limit scan to virtual region being asked Message-Id: <20150211140915.760d9737099fa0f1669818a8@linux-foundation.org> In-Reply-To: <20150114010830.GA16100@hori1.linux.bs1.fc.nec.co.jp> References: <1421152024-6204-1-git-send-email-shashim@codeaurora.org> <20150114010830.GA16100@hori1.linux.bs1.fc.nec.co.jp> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 14 Jan 2015 01:08:40 +0000 Naoya Horiguchi wrote: > On Tue, Jan 13, 2015 at 05:57:04PM +0530, Shiraz Hashim wrote: > > pagemap_read scans through the virtual address space of a > > task till it prepares 'count' pagemaps or it reaches end > > of task. > > > > This presents a problem when the page walk doesn't happen > > for vma with VM_PFNMAP set. In which case walk is silently > > skipped and no pagemap is prepare, in turn making > > pagemap_read to scan through task end, even crossing beyond > > 'count', landing into a different vma region. This leads to > > wrong presentation of mappings for that vma. > > > > Fix this by limiting end_vaddr to the end of the virtual > > address region being scanned. > > > > Signed-off-by: Shiraz Hashim > > This patch works in some case, but there still seems a problem in another case. > > Consider that we have two vmas within some narrow (PAGEMAP_WALK_SIZE) region. > One vma in lower address is VM_PFNMAP, and the other vma in higher address is not. > Then a single call of walk_page_range() skips the first vma and scans the > second vma, but the pagemap record of the second vma will be stored on the > wrong offset in the buffer, because we just skip vma(VM_PFNMAP) without calling > any callbacks (within which add_to_pagemap() increments pm.pos). > > So calling pte_hole() for vma(VM_PFNMAP) looks a better fix to me. > Can we get this finished off? ASAP, please.