CHMEM(8)                                                  System Administration                                                 CHMEM(8)

NAME
       chmem - configure memory

SYNOPSIS
       chmem [-h] [-V] [-v] [-e|-d] [SIZE|RANGE|-b BLOCKRANGE] [-z ZONE]

DESCRIPTION
       The chmem command sets a particular size or range of memory online or offline.

       ‐ Specify  SIZE as <size>[m|M|g|G]. With m or M, <size> specifies the memory size in MiB (1024 x 1024 bytes). With g or G, <size>
         specifies the memory size in GiB (1024 x 1024 x 1024 bytes). The default unit is MiB.

       ‐ Specify RANGE in the form 0x<start>-0x<end> as shown in the output of the lsmem command. <start> is the hexadecimal address  of
         the first byte and <end> is the hexadecimal address of the last byte in the memory range.

       ‐ Specify  BLOCKRANGE in the form <first>-<last> or <block> as shown in the output of the lsmem command. <first> is the number of
         the first memory block and <last> is the number of the last memory block in the memory range. Alternatively a single block  can
         be specified. BLOCKRANGE requires the --blocks option.

       ‐ Specify  ZONE as the name of a memory zone, as shown in the output of the lsmem -o +ZONES command. The output shows one or more
         valid memory zones for each memory range. If multiple zones are shown, then the memory range currently  belongs  to  the  first
         zone.  By  default,  chmem  will  set  memory online to the zone Movable, if this is among the valid zones. This default can be
         changed by specifying the --zone option with another valid zone.  For memory ballooning, it is recommended to select  the  zone
         Movable  for  memory  online and offline, if possible. Memory in this zone is much more likely to be able to be offlined again,
         but it cannot be used for arbitrary kernel allocations, only for migratable pages (e.g. anonymous and page cache  pages).   Use
         the --help option to see all available zones.

       SIZE and RANGE must be aligned to the Linux memory block size, as shown in the output of the lsmem command.

       Setting  memory  online  can  fail for various reasons. On virtualized systems it can fail if the hypervisor does not have enough
       memory left, for example because memory was overcommitted. Setting memory offline can fail if Linux cannot free  the  memory.  If
       only part of the requested memory can be set online or offline, a message tells you how much memory was set online or offline in‐
       stead of the requested amount.

       When setting memory online chmem starts with the lowest memory block numbers. When setting memory offline chmem starts  with  the
       highest memory block numbers.

OPTIONS
       -b, --blocks
              Use a BLOCKRANGE parameter instead of RANGE or SIZE for the --enable and --disable options.

       -d, --disable
              Set the specified RANGE, SIZE, or BLOCKRANGE of memory offline.

       -e, --enable
              Set the specified RANGE, SIZE, or BLOCKRANGE of memory online.

       -z, --zone
              Select the memory ZONE where to set the specified RANGE, SIZE, or BLOCKRANGE of memory online or offline. By default, mem‐
              ory will be set online to the zone Movable, if possible.

       -h, --help
              Print a short help text, then exit.

       -v, --verbose
              Verbose mode. Causes chmem to print debugging messages about it's progress.

       -V, --version
              Print the version number, then exit.

RETURN CODES
       chmem has the following return codes:

       0      success

       1      failure

       64     partial success

EXAMPLES
       chmem --enable 1024
              This command requests 1024 MiB of memory to be set online.

       chmem -e 2g
              This command requests 2 GiB of memory to be set online.

       chmem --disable 0x00000000e4000000-0x00000000f3ffffff
              This command requests the memory range starting with 0x00000000e4000000 and ending with 0x00000000f3ffffff to be set  off‐
              line.

       chmem -b -d 10
              This command requests the memory block number 10 to be set offline.

SEE ALSO
       lsmem(1)

AVAILABILITY
       The  chmem command is part of the util-linux package and is available from Linux Kernel Archive ⟨https://www.kernel.org/pub/linux
       /utils/util-linux/⟩.

util-linux                                                    October 2016                                                      CHMEM(8)

Usage:
 chmem [options] [SIZE|RANGE|BLOCKRANGE]

Set a particular size or range of memory online or offline.

Options:
 -e, --enable       enable memory
 -d, --disable      disable memory
 -b, --blocks       use memory blocks
 -z, --zone <name>  select memory zone (see below)
 -v, --verbose      verbose output
 -h, --help         display this help
 -V, --version      display version

Supported zones:
 DMA
 DMA32
 Normal
 Highmem
 Movable
 Device

For more details see chmem(8).