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Documentation/filesystems/proc.txt: add more description for maps/smaps

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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 <robert.hu@intel.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Xiao Guangrong <guangrong.xiao@linux.intel.com>
Cc: Robert Hu <robert.hu@intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Gleb Natapov <gleb@kernel.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Robert Ho 2016-10-07 17:02:39 -07:00 committed by Linus Torvalds
parent 855af072b6
commit 53aeee7a86
1 changed files with 12 additions and 0 deletions
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Documentation/filesystems/proc.txt
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@ -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).