CHMEM(8) System Administration CHMEM(8)
chmem - configure memory
chmem [-h] [-V] [-v] [-e|-d] [SIZE|RANGE|-b BLOCKRANGE] [-z ZONE]
The chmem command sets a particular size or range of memory online or
- 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
- 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
- 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. BLOCK-
RANGE 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 mem-
ory 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 recom-
mended 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 alloca-
tions, 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 sys-
tems 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 mem-
ory was set online or offline instead 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 mem-
ory block numbers.
Use a BLOCKRANGE parameter instead of RANGE or SIZE for the
--enable and --disable options.
Set the specified RANGE, SIZE, or BLOCKRANGE of memory offline.
Set the specified RANGE, SIZE, or BLOCKRANGE of memory online.
Select the memory ZONE where to set the specified RANGE, SIZE,
or BLOCKRANGE of memory online or offline. By default, memory
will be set online to the zone Movable, if possible.
Print a short help text, then exit.
Verbose mode. Causes chmem to print debugging messages about
Print the version number, then exit.
chmem has the following return codes:
64 partial success
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
chmem -b -d 10
This command requests the memory block number 10 to be set off-
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-
util-linux October 2016 CHMEM(8)
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