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Subject[PATCH 54 of 66] transparent hugepage config choice
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From: Andrea Arcangeli <aarcange@redhat.com>

Allow to choose between the always|madvise default for page faults and
khugepaged at config time. madvise guarantees zero risk of higher memory
footprint for applications (applications using madvise(MADV_HUGEPAGE) won't
risk to use any more memory by backing their virtual regions with hugepages).

Initially set the default to N and don't depend on EMBEDDED.

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---

diff --git a/mm/Kconfig b/mm/Kconfig
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -303,9 +303,8 @@ config NOMMU_INITIAL_TRIM_EXCESS
See Documentation/nommu-mmap.txt for more information.

config TRANSPARENT_HUGEPAGE
- bool "Transparent Hugepage Support" if EMBEDDED
+ bool "Transparent Hugepage Support"
depends on X86 && MMU
- default y
help
Transparent Hugepages allows the kernel to use huge pages and
huge tlb transparently to the applications whenever possible.
@@ -316,6 +315,30 @@ config TRANSPARENT_HUGEPAGE

If memory constrained on embedded, you may want to say N.

+choice
+ prompt "Transparent Hugepage Support sysfs defaults"
+ depends on TRANSPARENT_HUGEPAGE
+ default TRANSPARENT_HUGEPAGE_ALWAYS
+ help
+ Selects the sysfs defaults for Transparent Hugepage Support.
+
+ config TRANSPARENT_HUGEPAGE_ALWAYS
+ bool "always"
+ help
+ Enabling Transparent Hugepage always, can increase the
+ memory footprint of applications without a guaranteed
+ benefit but it will work automatically for all applications.
+
+ config TRANSPARENT_HUGEPAGE_MADVISE
+ bool "madvise"
+ help
+ Enabling Transparent Hugepage madvise, will only provide a
+ performance improvement benefit to the applications using
+ madvise(MADV_HUGEPAGE) but it won't risk to increase the
+ memory footprint of applications without a guaranteed
+ benefit.
+endchoice
+
#
# UP and nommu archs use km based percpu allocator
#
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -27,7 +27,12 @@
* allocations.
*/
unsigned long transparent_hugepage_flags __read_mostly =
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE_ALWAYS
(1<<TRANSPARENT_HUGEPAGE_FLAG)|
+#endif
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
+ (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
+#endif
(1<<TRANSPARENT_HUGEPAGE_DEFRAG_FLAG)|
(1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG);


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