From 53aeee7a86620b4dca81f6b807b37f36e7f99b09 Mon Sep 17 00:00:00 2001 From: Robert Ho Date: Fri, 7 Oct 2016 17:02:39 -0700 Subject: [PATCH] Documentation/filesystems/proc.txt: add more description for maps/smaps Add some more description on the limitations for smaps/maps readings, as well as some guaruntees we can make. Link: http://lkml.kernel.org/r/1475296958-27652-2-git-send-email-robert.hu@intel.com Signed-off-by: Robert Ho Acked-by: Michal Hocko Cc: Dave Hansen Cc: Xiao Guangrong Cc: Robert Hu Cc: Oleg Nesterov Cc: Paolo Bonzini Cc: Dan Williams Cc: Gleb Natapov Cc: Marcelo Tosatti Cc: Stefan Hajnoczi Cc: Ross Zwisler Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/filesystems/proc.txt | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index fcc1ac094282..219ffd41a911 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). -- 2.20.1