[PATCH] mm, vmacache: Add kconfig VMACACHE_SHIFT

[WANG Chao]

Add a new kconfig option VMACACHE_SHIFT (as a power of 2) to specify the
number of slots vma cache has for each thread. Range is chosen 0-4 (1-16
slots) to consider both overhead and performance penalty. Default is 2
(4 slots) as it originally is, which provides good enough balance.

Signed-off-by: WANG Chao <chaowang@xxxxxxxxxx>
---
 include/linux/sched.h | 2 +-
 mm/Kconfig            | 7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8db31ef..56fd96d 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -134,7 +134,7 @@ struct perf_event_context;
 struct blk_plug;
 struct filename;
 
-#define VMACACHE_BITS 2
+#define VMACACHE_BITS CONFIG_VMACACHE_SHIFT
 #define VMACACHE_SIZE (1U << VMACACHE_BITS)
 #define VMACACHE_MASK (VMACACHE_SIZE - 1)
 
diff --git a/mm/Kconfig b/mm/Kconfig
index 1d1ae6b..7b82a52 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -618,3 +618,10 @@ config MAX_STACK_SIZE_MB
 	  changed to a smaller value in which case that is used.
 
 	  A sane initial value is 80 MB.
+
+config VMACACHE_SHIFT
+	int "Number of slots in per-thread VMA cache (as a power of 2)"
+	range 0 4
+	default 2
+	help
+	  This is the number of slots VMA cache has for each thread.
-- 
2.1.0

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