[PATCH v4 2/2] Dcumentation/filesystems/proc.txt: Add more description for maps/smaps

From: Robert Ho
Date: Sat Oct 01 2016 - 00:43:42 EST

Add some more description on the limitations for smaps/maps readings, as well
as some guaruntees we can make.

Adopt Dave Hansen's revision from v1 as the description.

Signed-off-by: Robert Ho <robert.hu@xxxxxxxxx>
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

+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
+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).