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NAME | DESCRIPTION | SEE ALSO | COLOPHON |
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proc_meminfo(5) File Formats Manual proc_meminfo(5)
/proc/meminfo - memory usage
/proc/meminfo
This file reports statistics about memory usage on the
system. It is used by free(1) to report the amount of free
and used memory (both physical and swap) on the system as
well as the shared memory and buffers used by the kernel.
Each line of the file consists of a parameter name,
followed by a colon, the value of the parameter, and an
option unit of measurement (e.g., "kB"). The list below
describes the parameter names and the format specifier
required to read the field value. Except as noted below,
all of the fields have been present since at least Linux
2.6.0. Some fields are displayed only if the kernel was
configured with various options; those dependencies are
noted in the list.
MemTotal %lu
Total usable RAM (i.e., physical RAM minus a few
reserved bits and the kernel binary code).
MemFree %lu
The sum of LowFree+HighFree.
MemAvailable %lu (since Linux 3.14)
An estimate of how much memory is available for
starting new applications, without swapping.
Buffers %lu
Relatively temporary storage for raw disk blocks
that shouldn't get tremendously large (20 MB or so).
Cached %lu
In-memory cache for files read from the disk (the
page cache). Doesn't include SwapCached.
SwapCached %lu
Memory that once was swapped out, is swapped back in
but still also is in the swap file. (If memory
pressure is high, these pages don't need to be
swapped out again because they are already in the
swap file. This saves I/O.)
Active %lu
Memory that has been used more recently and usually
not reclaimed unless absolutely necessary.
Inactive %lu
Memory which has been less recently used. It is
more eligible to be reclaimed for other purposes.
Active(anon) %lu (since Linux 2.6.28)
[To be documented.]
Inactive(anon) %lu (since Linux 2.6.28)
[To be documented.]
Active(file) %lu (since Linux 2.6.28)
[To be documented.]
Inactive(file) %lu (since Linux 2.6.28)
[To be documented.]
Unevictable %lu (since Linux 2.6.28)
(From Linux 2.6.28 to Linux 2.6.30,
CONFIG_UNEVICTABLE_LRU was required.) [To be
documented.]
Mlocked %lu (since Linux 2.6.28)
(From Linux 2.6.28 to Linux 2.6.30,
CONFIG_UNEVICTABLE_LRU was required.) [To be
documented.]
HighTotal %lu
(Starting with Linux 2.6.19, CONFIG_HIGHMEM is
required.) Total amount of highmem. Highmem is all
memory above ~860 MB of physical memory. Highmem
areas are for use by user-space programs, or for the
page cache. The kernel must use tricks to access
this memory, making it slower to access than lowmem.
HighFree %lu
(Starting with Linux 2.6.19, CONFIG_HIGHMEM is
required.) Amount of free highmem.
LowTotal %lu
(Starting with Linux 2.6.19, CONFIG_HIGHMEM is
required.) Total amount of lowmem. Lowmem is
memory which can be used for everything that highmem
can be used for, but it is also available for the
kernel's use for its own data structures. Among
many other things, it is where everything from Slab
is allocated. Bad things happen when you're out of
lowmem.
LowFree %lu
(Starting with Linux 2.6.19, CONFIG_HIGHMEM is
required.) Amount of free lowmem.
MmapCopy %lu (since Linux 2.6.29)
(CONFIG_MMU is required.) [To be documented.]
SwapTotal %lu
Total amount of swap space available.
SwapFree %lu
Amount of swap space that is currently unused.
Dirty %lu
Memory which is waiting to get written back to the
disk.
Writeback %lu
Memory which is actively being written back to the
disk.
AnonPages %lu (since Linux 2.6.18)
Non-file backed pages mapped into user-space page
tables.
Mapped %lu
Files which have been mapped into memory (with
mmap(2)), such as libraries.
Shmem %lu (since Linux 2.6.32)
Amount of memory consumed in tmpfs(5) filesystems,
System V, and POSIX shared memory, as well as shared
anonymous mappings (MAP_SHARED|MAP_ANONYMOUS).
KReclaimable %lu (since Linux 4.20)
Kernel allocations that the kernel will attempt to
reclaim under memory pressure. Includes
SReclaimable (below), and other direct allocations
with a shrinker.
Slab %lu
In-kernel data structures cache. (See slabinfo(5).)
SReclaimable %lu (since Linux 2.6.19)
Part of Slab, that might be reclaimed, such as
caches.
SUnreclaim %lu (since Linux 2.6.19)
Part of Slab, that cannot be reclaimed on memory
pressure.
KernelStack %lu (since Linux 2.6.32)
Amount of memory allocated to kernel stacks.
PageTables %lu (since Linux 2.6.18)
Amount of memory dedicated to the lowest level of
page tables.
Quicklists %lu (since Linux 2.6.27)
(CONFIG_QUICKLIST is required.) [To be documented.]
NFS_Unstable %lu (since Linux 2.6.18)
NFS pages sent to the server, but not yet committed
to stable storage.
Bounce %lu (since Linux 2.6.18)
Memory used for block device "bounce buffers".
WritebackTmp %lu (since Linux 2.6.26)
Memory used by FUSE for temporary writeback buffers.
CommitLimit %lu (since Linux 2.6.10)
This is the total amount of memory currently
available to be allocated on the system, expressed
in kilobytes. This limit is adhered to only if
strict overcommit accounting is enabled (mode 2 in
/proc/sys/vm/overcommit_memory). The limit is
calculated according to the formula described under
/proc/sys/vm/overcommit_memory. For further
details, see the kernel source file
Documentation/vm/overcommit-accounting.rst.
Committed_AS %lu
The amount of memory presently allocated on the
system. The committed memory is a sum of all of the
memory which has been allocated by processes, even
if it has not been "used" by them as of yet. A
process which allocates 1 GB of memory (using
malloc(3) or similar), but touches only 300 MB of
that memory will show up as using only 300 MB of
memory even if it has the address space allocated
for the entire 1 GB.
This 1 GB is memory which has been "committed" to by
the VM and can be used at any time by the allocating
application. With strict overcommit enabled on the
system (mode 2 in /proc/sys/vm/overcommit_memory),
allocations which would exceed the CommitLimit will
not be permitted. This is useful if one needs to
guarantee that processes will not fail due to lack
of memory once that memory has been successfully
allocated.
VmallocTotal %lu
Total size of vmalloc memory area.
VmallocUsed %lu
Amount of vmalloc area which is used. Since Linux
4.4, this field is no longer calculated, and is hard
coded as 0. See /proc/vmallocinfo.
VmallocChunk %lu
Largest contiguous block of vmalloc area which is
free. Since Linux 4.4, this field is no longer
calculated and is hard coded as 0. See
/proc/vmallocinfo.
HardwareCorrupted %lu (since Linux 2.6.32)
(CONFIG_MEMORY_FAILURE is required.) [To be
documented.]
LazyFree %lu (since Linux 4.12)
Shows the amount of memory marked by madvise(2)
MADV_FREE.
AnonHugePages %lu (since Linux 2.6.38)
(CONFIG_TRANSPARENT_HUGEPAGE is required.) Non-file
backed huge pages mapped into user-space page
tables.
ShmemHugePages %lu (since Linux 4.8)
(CONFIG_TRANSPARENT_HUGEPAGE is required.) Memory
used by shared memory (shmem) and tmpfs(5) allocated
with huge pages.
ShmemPmdMapped %lu (since Linux 4.8)
(CONFIG_TRANSPARENT_HUGEPAGE is required.) Shared
memory mapped into user space with huge pages.
CmaTotal %lu (since Linux 3.1)
Total CMA (Contiguous Memory Allocator) pages.
(CONFIG_CMA is required.)
CmaFree %lu (since Linux 3.1)
Free CMA (Contiguous Memory Allocator) pages.
(CONFIG_CMA is required.)
HugePages_Total %lu
(CONFIG_HUGETLB_PAGE is required.) The size of the
pool of huge pages.
HugePages_Free %lu
(CONFIG_HUGETLB_PAGE is required.) The number of
huge pages in the pool that are not yet allocated.
HugePages_Rsvd %lu (since Linux 2.6.17)
(CONFIG_HUGETLB_PAGE is required.) This is the
number of huge pages for which a commitment to
allocate from the pool has been made, but no
allocation has yet been made. These reserved huge
pages guarantee that an application will be able to
allocate a huge page from the pool of huge pages at
fault time.
HugePages_Surp %lu (since Linux 2.6.24)
(CONFIG_HUGETLB_PAGE is required.) This is the
number of huge pages in the pool above the value in
/proc/sys/vm/nr_hugepages. The maximum number of
surplus huge pages is controlled by
/proc/sys/vm/nr_overcommit_hugepages.
Hugepagesize %lu
(CONFIG_HUGETLB_PAGE is required.) The size of huge
pages.
DirectMap4k %lu (since Linux 2.6.27)
Number of bytes of RAM linearly mapped by kernel in
4 kB pages. (x86.)
DirectMap4M %lu (since Linux 2.6.27)
Number of bytes of RAM linearly mapped by kernel in
4 MB pages. (x86 with CONFIG_X86_64 or
CONFIG_X86_PAE enabled.)
DirectMap2M %lu (since Linux 2.6.27)
Number of bytes of RAM linearly mapped by kernel in
2 MB pages. (x86 with neither CONFIG_X86_64 nor
CONFIG_X86_PAE enabled.)
DirectMap1G %lu (since Linux 2.6.27)
(x86 with CONFIG_X86_64 and
CONFIG_X86_DIRECT_GBPAGES enabled.)
proc(5)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
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⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
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man-pages@man7.org
Linux man-pages 6.15 2025-05-24 proc_meminfo(5)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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