proc_meminfo(5) — Linux manual page

NAME | DESCRIPTION | SEE ALSO | COLOPHON

proc_meminfo(5)            File Formats Manual           proc_meminfo(5)

NAME         top

       /proc/meminfo - memory usage

DESCRIPTION         top

       /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.

              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.)

SEE ALSO         top

       proc(5)

COLOPHON         top

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Linux man-pages 6.9.1          2024-05-02                proc_meminfo(5)