From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f69.google.com (mail-pa0-f69.google.com [209.85.220.69]) by kanga.kvack.org (Postfix) with ESMTP id 85A286B025E for ; Sat, 1 Oct 2016 00:43:17 -0400 (EDT) Received: by mail-pa0-f69.google.com with SMTP id bv10so233224076pad.2 for ; Fri, 30 Sep 2016 21:43:17 -0700 (PDT) Received: from mga03.intel.com (mga03.intel.com. [134.134.136.65]) by mx.google.com with ESMTPS id u63si18378107pfa.1.2016.09.30.21.43.16 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 30 Sep 2016 21:43:16 -0700 (PDT) From: Robert Ho Subject: [PATCH v4 2/2] Dcumentation/filesystems/proc.txt: Add more description for maps/smaps Date: Sat, 1 Oct 2016 12:42:38 +0800 Message-Id: <1475296958-27652-2-git-send-email-robert.hu@intel.com> In-Reply-To: <1475296958-27652-1-git-send-email-robert.hu@intel.com> References: <1475296958-27652-1-git-send-email-robert.hu@intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: pbonzini@redhat.com, akpm@linux-foundation.org, mhocko@suse.com, oleg@redhat.com, dave.hansen@intel.com, dan.j.williams@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, Robert Ho 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 --- 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 -- 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