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 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 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 memory block numbers.
- -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,
memory 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.
chmem has the following return codes:
- 0
- success
- 1
- failure
- 64
- partial success