[PATCH v2 7/7] mm: Add config HUGE_IOMAP to enable huge I/O mappings

[Toshi Kani]

Add config HUGE_IOMAP to enable huge I/O mappings.  This feature
is set to Y by default when HAVE_ARCH_HUGE_VMAP is defined on the
architecture.

Note that user can also disable this feature at boot-time by the
new kernel option "nohugeiomap" when necessary.

Signed-off-by: Toshi Kani <toshi.kani@xxxxxx>
---
 mm/Kconfig |   11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/mm/Kconfig b/mm/Kconfig
index 1d1ae6b..eb738ae 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -444,6 +444,17 @@ choice
 	  benefit.
 endchoice
 
+config HUGE_IOMAP
+	bool "Kernel huge I/O mapping support"
+	depends on HAVE_ARCH_HUGE_VMAP
+	default y
+	help
+	  Kernel huge I/O mapping allows the kernel to transparently
+	  create I/O mappings with huge pages for memory-mapped I/O
+	  devices whenever possible.  This feature can improve
+	  performance of certain devices with large memory size, such
+	  as NVM, and reduce the time to create their mappings.
+
 #
 # UP and nommu archs use km based percpu allocator
 #
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