From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1035238AbcIWQGN (ORCPT ); Fri, 23 Sep 2016 12:06:13 -0400 Received: from mga02.intel.com ([134.134.136.20]:32667 "EHLO mga02.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030326AbcIWQGL (ORCPT ); Fri, 23 Sep 2016 12:06:11 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.30,382,1470726000"; d="scan'208";a="883115367" Subject: Re: [PATCH v3 2/2] Documentation/filesystems/proc.txt: Add more description for maps/smaps To: Robert Ho , pbonzini@redhat.com, akpm@linux-foundation.org, mhocko@suse.com, oleg@redhat.com, dan.j.williams@intel.com References: <1474636354-25573-1-git-send-email-robert.hu@intel.com> <1474636354-25573-2-git-send-email-robert.hu@intel.com> Cc: 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 From: Dave Hansen Message-ID: <57E552F2.4030302@intel.com> Date: Fri, 23 Sep 2016 09:06:10 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0 MIME-Version: 1.0 In-Reply-To: <1474636354-25573-2-git-send-email-robert.hu@intel.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/23/2016 06:12 AM, Robert Ho wrote: > +Note: for both /proc/PID/maps and /proc/PID/smaps readings, it's > +possible in race conditions, that the mappings printed may not be that > +up-to-date, because during each read walking, the task's mappings may have > +changed, this typically happens in multithread cases. But anyway in each single > +read these can be guarunteed: 1) the mapped addresses doesn't go backward; 2) no > +overlaps 3) 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. Could we spuce this description up a bit? Perhaps: Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy. 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.