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(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.
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 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, memory will be set online to the zone Movable, if possible.
-v, --verbose
Verbose mode. Causes chmem to print debugging
messages about it’s progress.
-h, --help
Display help text and exit.
-V, --version
Print version and exit.
EXIT STATUS¶
chmem has the following exit status values:
0
success
1
failure
64
partial success
EXAMPLE¶
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 offline.
chmem -b -d 10
This command requests the memory block number 10 to be
set offline.