Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752072AbcJAEnh (ORCPT ); Sat, 1 Oct 2016 00:43:37 -0400 Received: from mga06.intel.com ([134.134.136.31]:10861 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751490AbcJAEnS (ORCPT ); Sat, 1 Oct 2016 00:43:18 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.31,424,1473145200"; d="scan'208";a="15157669" From: Robert Ho 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 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> X-Mailer: git-send-email 1.8.3.1 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: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1457 Lines: 37 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