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>

2 files changed, 30 insertions, 2 deletions

diff --git a/mm/Kconfig b/mm/Kconfig
index d774f77538ce..3e81687263b5 100644
--- 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 bce6e12140e2..30c3cec82023 100644
--- 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);