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 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,
−−blocksUse a BLOCKRANGE parameter
instead of RANGE or SIZE for the −−enable and −−disable options.
−d,
−−disableSet the specified RANGE, SIZE, or BLOCKRANGE of memory
offline.
−e,
−−enableSet the specified RANGE, SIZE, or BLOCKRANGE of memory
online.
−z,
−−zoneSelect 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,
−−helpPrint a short help text, then exit.
−v,
−−verboseVerbose mode. Causes chmem to print debugging messages about it's progress.
−V,
−−versionPrint the version number, then exit.
This command requests 1024 MiB of memory to be set online.
This command requests 2 GiB of memory to be set online.
This command requests the memory range starting with 0x00000000e4000000 and ending with 0x00000000f3ffffff to be set offline.
This command requests the memory block number 10 to be set offline.
The chmem command is part of the util-linux package and is available from Linux Kernel Archive
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