thp: transparent hugepage config choice

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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/Kconfig b/mm/Kconfig
index d774f77..3e81687 100644 (file)
--- 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
index bce6e12..30c3cec 100644 (file)
--- 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);