proc_pid_pagemap(5)

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/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.

NAME

/proc/pid/pagemap - mapping of virtual pages

/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).