s390/vmcp: make use of contiguous memory allocator

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 <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/drivers/s390/char/Kconfig b/drivers/s390/char/Kconfig
index b3f1c45..97c4c9f 100644
--- a/drivers/s390/char/Kconfig
+++ b/drivers/s390/char/Kconfig
@@ -169,10 +169,21 @@ config VMCP
 	def_bool y
 	prompt "Support for the z/VM CP interface"
 	depends on S390
+	select CMA
 	help
 	  Select this option if you want to be able to interact with the control
 	  program on z/VM
 
+config VMCP_CMA_SIZE
+	int "Memory in MiB reserved for z/VM CP interface"
+	default "4"
+	depends on VMCP
+	help
+	  Specify the default amount of memory in MiB reserved for the z/VM CP
+	  interface. If needed this memory is used for large contiguous memory
+	  allocations. The default can be changed with the kernel command line
+	  parameter "vmcp_cma".
+
 config MONREADER
 	def_tristate m
 	prompt "API for reading z/VM monitor service records"