NAME

       /proc/pid/pagemap - mapping of virtual pages

DESCRIPTION

       /proc/pid/pagemap (since Linux 2.6.25)
              This  file  shows  the mapping of each of the process's virtual pages into physical
              page frames or swap area.  It contains one 64-bit value for each virtual page, with
              the bits set as follows:

              63     If set, the page is present in RAM.

              62     If set, the page is in swap space

              61 (since Linux 3.5)
                     The page is a file-mapped page or a shared anonymous page.

              60–58 (since Linux 3.11)
                     Zero

              57 (since Linux 5.14)
                     If set, the page is write-protected through userfaultfd(2).

              56 (since Linux 4.2)
                     The page is exclusively mapped.

              55 (since Linux 3.11)
                     PTE      is      soft-dirty      (see     the     kernel     source     file
                     Documentation/admin-guide/mm/soft-dirty.rst).

              54–0   If the page is present in RAM (bit 63), then these  bits  provide  the  page
                     frame   number,   which   can   be   used   to  index  /proc/kpageflags  and
                     /proc/kpagecount.  If the page is present in swap (bit 62),  then  bits  4–0
                     give the swap type, and bits 54–5 encode the swap offset.

              Before Linux 3.11, bits 60–55 were used to encode the base-2 log of the page size.

              To  employ  /proc/pid/pagemap  efficiently,  use  /proc/pid/maps to determine which
              areas of memory are actually mapped and seek to skip over unmapped regions.

              The /proc/pid/pagemap file is present only if the  CONFIG_PROC_PAGE_MONITOR  kernel
              configuration option is enabled.

              Permission   to   access   this   file   is   governed  by  a  ptrace  access  mode
              PTRACE_MODE_READ_FSCREDS check; see ptrace(2).

SEE ALSO

       proc(5)