The patch titled
Subject: Documentation/filesystems/proc.txt: add more description for maps/smaps
has been added to the -mm tree. Its filename is
dcumentation-filesystems-proctxt-add-more-description-for-maps-smaps.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/dcumentation-filesystems-proctxt-add-more-description-for-maps-smaps.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/dcumentation-filesystems-proctxt-add-more-description-for-maps-smaps.patch
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------------------------------------------------------
From: Robert Ho <robert.hu@xxxxxxxxx>
Subject: 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@xxxxxxxxx
Signed-off-by: Robert Ho <robert.hu@xxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Xiao Guangrong <guangrong.xiao@xxxxxxxxxxxxxxx>
Cc: Robert Hu <robert.hu@xxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Gleb Natapov <gleb@xxxxxxxxxx>
Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
Cc: Stefan Hajnoczi <stefanha@xxxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/filesystems/proc.txt | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff -puN Documentation/filesystems/proc.txt~dcumentation-filesystems-proctxt-add-more-description-for-maps-smaps Documentation/filesystems/proc.txt
--- a/Documentation/filesystems/proc.txt~dcumentation-filesystems-proctxt-add-more-description-for-maps-smaps
+++ a/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).
_
Patches currently in -mm which might be from robert.hu@xxxxxxxxx are
mm-proc-fix-region-lost-in-proc-self-smaps.patch
dcumentation-filesystems-proctxt-add-more-description-for-maps-smaps.patch
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