chmem(8) - phpMan

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 speci-
fied. 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 mul-
tiple 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 overcom-
mitted. 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 Mov-
able, 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 offline.

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