From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753101AbcJCLyG (ORCPT ); Mon, 3 Oct 2016 07:54:06 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:36698 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752232AbcJCLx6 (ORCPT ); Mon, 3 Oct 2016 07:53:58 -0400 Date: Mon, 3 Oct 2016 13:53:55 +0200 From: Michal Hocko To: Robert Ho Cc: pbonzini@redhat.com, akpm@linux-foundation.org, oleg@redhat.com, dave.hansen@intel.com, dan.j.williams@intel.com, guangrong.xiao@linux.intel.com, gleb@kernel.org, mtosatti@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, stefanha@redhat.com, yuhuang@redhat.com, linux-mm@kvack.org, ross.zwisler@linux.intel.com Subject: Re: [PATCH v4 2/2] Dcumentation/filesystems/proc.txt: Add more description for maps/smaps Message-ID: <20161003115355.GB26768@dhcp22.suse.cz> References: <1475296958-27652-1-git-send-email-robert.hu@intel.com> <1475296958-27652-2-git-send-email-robert.hu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1475296958-27652-2-git-send-email-robert.hu@intel.com> User-Agent: Mutt/1.6.0 (2016-04-01) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat 01-10-16 12:42:38, Robert Ho wrote: > Add some more description on the limitations for smaps/maps readings, as well > as some guaruntees we can make. > > Changelog: > v2: > Adopt Dave Hansen's revision from v1 as the description. > > Signed-off-by: Robert Ho Acked-by: Michal Hocko > --- > Documentation/filesystems/proc.txt | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt > index 68080ad..daa096f 100644 > --- a/Documentation/filesystems/proc.txt > +++ b/Documentation/filesystems/proc.txt > @@ -515,6 +515,18 @@ be vanished or the reverse -- new added. > This file is only present if the CONFIG_MMU kernel configuration option is > enabled. > > +Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent > +output can be achieved only in the single read call). > +This typically manifests when doing partial reads of these files while the > +memory map is being modified. Despite the races, we do provide the following > +guarantees: > + > +1) The mapped addresses never go backwards, which implies no two > + regions will ever overlap. > +2) If there is something at a given vaddr during the entirety of the > + life of the smaps/maps walk, there will be some output for it. > + > + > The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG > bits on both physical and virtual pages associated with a process, and the > soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details). > -- > 1.8.3.1 > -- Michal Hocko SUSE Labs