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>
diff --git a/mm/memory.c b/mm/memory.c
index 712790e..4425b60 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2920,7 +2920,7 @@
return 0;
}
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
#define HPAGE_CACHE_INDEX_MASK (HPAGE_PMD_NR - 1)
static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
@@ -3002,7 +3002,8 @@
pte_t entry;
int ret;
- if (pmd_none(*fe->pmd) && PageTransCompound(page)) {
+ if (pmd_none(*fe->pmd) && PageTransCompound(page) &&
+ IS_ENABLED(CONFIG_TRANSPARENT_HUGE_PAGECACHE)) {
/* THP on COW? */
VM_BUG_ON_PAGE(memcg, page);