From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752245AbaHAHCB (ORCPT ); Fri, 1 Aug 2014 03:02:01 -0400 Received: from mail-lb0-f182.google.com ([209.85.217.182]:47852 "EHLO mail-lb0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750703AbaHAHCA (ORCPT ); Fri, 1 Aug 2014 03:02:00 -0400 Date: Fri, 1 Aug 2014 11:01:56 +0400 From: Cyrill Gorcunov To: Peter Feiner Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Pavel Emelyanov , Hugh Dickins , Naoya Horiguchi , Andrew Morton Subject: Re: [PATCH] mm: softdirty: respect VM_SOFTDIRTY in PTE holes Message-ID: <20140801070156.GE17343@moon> References: <1406846605-12176-1-git-send-email-pfeiner@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1406846605-12176-1-git-send-email-pfeiner@google.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 31, 2014 at 06:43:25PM -0400, Peter Feiner wrote: > After a VMA is created with the VM_SOFTDIRTY flag set, > /proc/pid/pagemap should report that the VMA's virtual pages are > soft-dirty until VM_SOFTDIRTY is cleared (i.e., by the next write of > "4" to /proc/pid/clear_refs). However, pagemap ignores the > VM_SOFTDIRTY flag for virtual addresses that fall in PTE holes (i.e., > virtual addresses that don't have a PMD, PUD, or PGD allocated yet). > > To observe this bug, use mmap to create a VMA large enough such that > there's a good chance that the VMA will occupy an unused PMD, then > test the soft-dirty bit on its pages. In practice, I found that a VMA > that covered a PMD's worth of address space was big enough. > > This patch adds the necessary VMA lookup to the PTE hole callback in > /proc/pid/pagemap's page walk and sets soft-dirty according to the > VMAs' VM_SOFTDIRTY flag. > > Signed-off-by: Peter Feiner Acked-by: Cyrill Gorcunov