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).