proc_pid_smaps - Man Page

XXX: What does 's' in "smaps" stand for?


/proc/pid/smaps (since Linux 2.6.14)

This file shows memory consumption for each of the process's mappings. (The pmap(1) command displays similar information, in a form that may be easier for parsing.) For each mapping there is a series of lines such as the following:

00400000-0048a000 r-xp 00000000 fd:03 960637       /bin/bash
Size:                552 kB
Rss:                 460 kB
Pss:                 100 kB
Shared_Clean:        452 kB
Shared_Dirty:          0 kB
Private_Clean:         8 kB
Private_Dirty:         0 kB
Referenced:          460 kB
Anonymous:             0 kB
AnonHugePages:         0 kB
ShmemHugePages:        0 kB
ShmemPmdMapped:        0 kB
Swap:                  0 kB
KernelPageSize:        4 kB
MMUPageSize:           4 kB
Locked:                0 kB
ProtectionKey:         0
VmFlags: rd ex mr mw me dw

The first of these lines shows the same information as is displayed for the mapping in /proc/pid/maps. The following lines show the size of the mapping, the amount of the mapping that is currently resident in RAM ("Rss"), the process's proportional share of this mapping ("Pss"), the number of clean and dirty shared pages in the mapping, and the number of clean and dirty private pages in the mapping. "Referenced" indicates the amount of memory currently marked as referenced or accessed. "Anonymous" shows the amount of memory that does not belong to any file. "Swap" shows how much would-be-anonymous memory is also used, but out on swap.

The "KernelPageSize" line (available since Linux 2.6.29) is the page size used by the kernel to back the virtual memory area. This matches the size used by the MMU in the majority of cases. However, one counter-example occurs on PPC64 kernels whereby a kernel using 64 kB as a base page size may still use 4 kB pages for the MMU on older processors. To distinguish the two attributes, the "MMUPageSize" line (also available since Linux 2.6.29) reports the page size used by the MMU.

The "Locked" indicates whether the mapping is locked in memory or not.

The "ProtectionKey" line (available since Linux 4.9, on x86 only) contains the memory protection key (see pkeys(7)) associated with the virtual memory area. This entry is present only if the kernel was built with the CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS configuration option (since Linux 4.6).

The "VmFlags" line (available since Linux 3.8) represents the kernel flags associated with the virtual memory area, encoded using the following two-letter codes:

mr-may read
mw-may write
me-may execute
ms-may share
gd-stack segment grows down
pf-pure PFN range
dw-disabled write to the mapped file
lo-pages are locked in memory
io-memory mapped I/O area
sr-sequential read advise provided
rr-random read advise provided
dc-do not copy area on fork
de-do not expand area on remapping
ac-area is accountable
nr-swap space is not reserved for the area
ht-area uses huge tlb pages
sf-perform synchronous page faults (since Linux 4.15)
nl-non-linear mapping (removed in Linux 4.0)
ar-architecture specific flag
wf-wipe on fork (since Linux 4.14)
dd-do not include area into core dump
sd-soft-dirty flag (since Linux 3.13)
mm-mixed map area
hg-huge page advise flag
nh-no-huge page advise flag
mg-mergeable advise flag
um-userfaultfd missing pages tracking (since Linux 4.3)
uw-userfaultfd wprotect pages tracking (since Linux 4.3)

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

See Also



2023-09-07 Linux man-pages 6.7