thp: introduce CONFIG_TRANSPARENT_HUGE_PAGECACHE

For file mappings, we don't deposit page tables on THP allocation
because it's not strictly required to implement split_huge_pmd(): we can
just clear pmd and let following page faults to reconstruct the page
table.

But Power makes use of deposited page table to address MMU quirk.

Let's hide THP page cache, including huge tmpfs, under separate config
option, so it can be forbidden on Power.

We can revert the patch later once solution for Power found.

Link: http://lkml.kernel.org/r/1466021202-61880-36-git-send-email-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/mm/Kconfig b/mm/Kconfig
index 3e2daef..3c81803 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -440,6 +440,14 @@ choice
 endchoice
 
 #
+# We don't deposit page tables on file THP mapping,
+# but Power makes use of them to address MMU quirk.
+#
+config	TRANSPARENT_HUGE_PAGECACHE
+	def_bool y
+	depends on TRANSPARENT_HUGEPAGE && !PPC
+
+#
 # UP and nommu archs use km based percpu allocator
 #
 config NEED_PER_CPU_KM