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s390/vmcp: make use of contiguous memory allocator

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If memory is fragmented it is unlikely that large order memory
allocations succeed. This has been an issue with the vmcp device
driver since a long time, since it requires large physical contiguous
memory ares for large responses.

To hopefully resolve this issue make use of the contiguous memory
allocator (cma). This patch adds a vmcp specific vmcp cma area with a
default size of 4MB. The size can be changed either via the
VMCP_CMA_SIZE config option at compile time or with the "vmcp_cma"
kernel parameter (e.g. "vmcp_cma=16m").

For any vmcp response buffers larger than 16k memory from the cma area
will be allocated. If such an allocation fails, there is a fallback to
the buddy allocator.

Signed-off-by: Heiko Carstens <[email protected]>
Signed-off-by: Martin Schwidefsky <[email protected]>
This commit is contained in:
Heiko Carstens 2017-08-07 15:16:15 +02:00 • committed by Martin Schwidefsky
commit 3f4298427a
6 changed files with 90 additions and 9 deletions
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4
Documentation/admin-guide/kernel-parameters.txt
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@ -4375,6 +4375,10 @@
decrease the size and leave more room for directly
mapped kernel RAM.
vmcp_cma=nn[MG] [KNL,S390]
Sets the memory size reserved for contiguous memory
allocations for the vmcp device driver.
vmhalt= [KNL,S390] Perform z/VM CP command after system halt.
Format: <command>