| Message ID | 1475296958-27652-2-git-send-email-robert.hu@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Sat 01-10-16 12:42:38, Robert Ho wrote: > 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 <robert.hu@intel.com> Acked-by: Michal Hocko <mhocko@suse.com> > --- > 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 >
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).
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 <robert.hu@intel.com> --- Documentation/filesystems/proc.txt | 12 ++++++++++++ 1 file changed, 12 insertions(+)