[RFC v2 10/10] mm: Introduce CONFIG_MEM_RANGE_LOCK

[Laurent Dufour <ldufour@linux.vnet.ibm.com>]

A new configuration variable is introduced to activate the use of
range lock instead of semaphore to protect per process memory layout.

This range lock is replacing the use of a semaphore for mmap_sem.

Currently only available for X86_64 and PPC64 architectures.

By default this option is turned off and requires the EXPERT mode
since it is not yet complete.

Signed-off-by: Laurent Dufour <ldufour@linux.vnet.ibm.com>
---
 mm/Kconfig | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/mm/Kconfig b/mm/Kconfig
index beb7a455915d..955d9a735a49 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -309,6 +309,18 @@ config NEED_BOUNCE_POOL
 	bool
 	default y if TILE && USB_OHCI_HCD
 
+config MEM_RANGE_LOCK
+	bool "Use range lock for process's memory layout"
+	default n
+	depends on EXPERT
+	depends on MMU
+	depends on X86_64 || PPC64
+	help
+	  Use range lock instead of traditional semaphore to protect per
+	  process memory layout. This is required when dealing with massive
+	  threaded process on very large system (more than 80 cpu threads).
+	  If unsure say n.
+
 config NR_QUICK
 	int
 	depends on QUICKLIST
-- 
2.7.4

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