proc_pid_clear_refs(5) File Formats Manual proc_pid_clear_refs(5)
NAME
/proc/pid/clear_refs - reset the PG_Referenced and ACCESSED/YOUNG bits
DESCRIPTION
/proc/pid/clear_refs (since Linux 2.6.22)
This is a write-only file, writable only by owner of the process.
The following values may be written to the file:
1 (since Linux 2.6.22)
Reset the PG_Referenced and ACCESSED/YOUNG bits for all
the pages associated with the process. (Before Linux
2.6.32, writing any nonzero value to this file had this
effect.)
2 (since Linux 2.6.32)
Reset the PG_Referenced and ACCESSED/YOUNG bits for all
anonymous pages associated with the process.
3 (since Linux 2.6.32)
Reset the PG_Referenced and ACCESSED/YOUNG bits for all
file-mapped pages associated with the process.
Clearing the PG_Referenced and ACCESSED/YOUNG bits provides a
method to measure approximately how much memory a process is us-
ing. One first inspects the values in the "Referenced" fields
for the VMAs shown in /proc/pid/smaps to get an idea of the mem-
ory footprint of the process. One then clears the PG_Referenced
and ACCESSED/YOUNG bits and, after some measured time interval,
once again inspects the values in the "Referenced" fields to get
an idea of the change in memory footprint of the process during
the measured interval. If one is interested only in inspecting
the selected mapping types, then the value 2 or 3 can be used in-
stead of 1.
Further values can be written to affect different properties:
4 (since Linux 3.11)
Clear the soft-dirty bit for all the pages associated with
the process. This is used (in conjunction with
/proc/pid/pagemap) by the check-point restore system to
discover which pages of a process have been dirtied since
the file /proc/pid/clear_refs was written to.
5 (since Linux 4.0)
Reset the peak resident set size ("high water mark") to
the process's current resident set size value.
Writing any value to /proc/pid/clear_refs other than those listed
above has no effect.
The /proc/pid/clear_refs file is present only if the CON-
FIG_PROC_PAGE_MONITOR kernel configuration option is enabled.
SEE ALSO
proc(5)
Linux man-pages 6.9.1 2024-05-02 proc_pid_clear_refs(5)
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