Задание по файловой системе /proc

[Evgeny Sinelnikov]

Здравствуйте,

высылаю пример разбора одного из файлов, описывающих свойства процесса в рамках составления списка значимых ресурсов процесса.

Рассмотрели на практике:

/proc/PID/clear_refs

Выяснили, что это файл, доступный только на запись, управляет состоянием виртуальной памятью процесса и к списку ресурсов фактически отношения не имеет.

• http://man7.org/linux/man-pages/man5/proc.5.html
• https://www.kernel.org/doc/Documentation/vm/soft-dirty.txt
• http://wiki.osdev.org/Paging
  

/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 kernel
                     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
              using.  One first inspects the values in the "Referenced"
              fields for the VMAs shown in /proc/[pid]/smaps to get an idea
              of the memory 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 instead of 1.

              A further value can be written to affect a different bit:

              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.

              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
              CONFIG_PROC_PAGE_MONITOR kernel configuration option is
              enabled.

--

Sin (Sinelnikov Evgeny)