chmem [-h] [-V] [-v]
[-c|-e|-d|-g]
[SIZE|RANGE|-b BLOCKRANGE] [-z
ZONE] [-m MEMMAP-ON-MEMORY]
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(1)
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(1) 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.
•Specify MEMMAP-ON-MEMORY as 1 or 0. A
value of 1 allocates hotplug metadata (such as the struct pages array) from
the hotplug memory itself, enabling hot-add operations even under memory
pressure and without requiring additional system memory to do so. A value of 0
stores hotplugged memory metadata in regular system memory, which helps avoid
issues related to fragmentation of continuous physical memory across memory
blocks. The value can only be set when the memory block is in a deconfigured
state, and --memmap-on-memory is valid only with --configure. If
not specified, and if supported, chmem uses the default value shown in
lsmem output.
The --enable option configures the memory, if this is
supported by the architecture. If configuring memory is not supported by the
architecture, --enable still brings the memory online.
The --disable option brings the memory offline and performs
an optional deconfigure step if this is supported by the architecture.
The --configure option requests memory from the hypervisor
without bringing it online, when supported by the architecture, allowing
explicit control and use of --memmap-on-memory.
The --deconfigure option returns memory resources to the
hypervisor if supported by the architecture.
SIZE and RANGE must be aligned to the Linux memory
block size, as shown in the output of the lsmem(1) 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 or when configuring memory,
chmem starts with the lowest memory block numbers. When setting
memory offline or deconfiguring memory, chmem starts with the highest
memory block numbers.
•s390 architecture:
MEMMAP-ON-MEMORY: For memory blocks configured online at
boot, the default value is 0 because they are added without memmap-on-memory
support. Memory added dynamically at runtime uses the default value
displayed in lsmem output.
-b, --blocks
Use a BLOCKRANGE parameter instead of RANGE
or SIZE for the --enable and --disable options.
-c, --configure
Set the specified RANGE, SIZE, or
BLOCKRANGE of memory to be configured.
-d, --disable
Set the specified RANGE, SIZE, or
BLOCKRANGE of memory offline.
-e, --enable
Set the specified RANGE, SIZE, or
BLOCKRANGE of memory online.
-g, --deconfigure
Set the specified RANGE, SIZE, or
BLOCKRANGE of memory to be deconfigured.
-m, --memmap-on-memory
Select memmap-on-memory for the specified RANGE,
SIZE, or BLOCKRANGE of memory. This option is valid only with
--configure.
-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.
-v, --verbose
Verbose mode. Causes chmem to print debugging
messages about its progress.
-h, --help
Display help text and exit.
-V, --version
Display version and exit.
chmem has the following exit status values:
0
success
1
failure
64
partial success
chmem --enable 1024
This command requests 1024 MiB of memory to be set
online.
chmem -e 2g
This command requests 2 GB of memory to be brought online
and, if supported by the architecture, configures the memory beforehand.
chmem --disable 0x00000000e4000000-0x00000000f3ffffff
This command takes the memory range from
0x00000000e4000000 to 0x00000000f3ffffff offline and deconfigures it if
supported by the architecture.
chmem -b -d 10
This command takes memory block number 10 offline.
chmem -b -c 10 -m 1
This command configures memory block 10 with
MEMMAP-ON-MEMORY set. The block must be in a deconfigured state.
chmem -b -c 10
This command configures memory block 10 with the default
MEMMAP-ON-MEMORY setting. The default value is displayed in lsmem
--output-all. The block must be in a deconfigured state.
chmem -b -g 10
This command deconfigures memory block 10. The block must
be offline.
chmem -d 5g
This command takes 5 GB of memory offline and
deconfigures it if supported by the architecture. Blocks that are already
offline but still configured are skipped and must be explicitly deconfigured
with --deconfigure.