[RFC PATCH 1/3] mm/thp: Use pmdp_splitting_flush_notify to clear pmd on splitting

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

Some arch may require an explicit IPI before a THP PMD split. This
ensures that a local_irq_disable can prevent a parallel THP PMD split.
So use new function which arch can override

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
---
 include/asm-generic/pgtable.h |  5 +++++
 mm/huge_memory.c              |  7 ++++---
 mm/pgtable-generic.c          | 11 +++++++++++
 3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index fe617b7e4be6..d091a666f5b1 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -184,6 +184,11 @@ static inline void pmdp_set_wrprotect(struct mm_struct *mm,
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
 
+#ifndef __HAVE_ARCH_PMDP_SPLITTING_FLUSH_NOTIFY
+extern void pmdp_splitting_flush_notify(struct vm_area_struct *vma,
+					unsigned long address, pmd_t *pmdp);
+#endif
+
 #ifndef __HAVE_ARCH_PGTABLE_DEPOSIT
 extern void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,
 				       pgtable_t pgtable);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index cce4604c192f..81e9578bf43a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2606,9 +2606,10 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 
 	write = pmd_write(*pmd);
 	young = pmd_young(*pmd);
-
-	/* leave pmd empty until pte is filled */
-	pmdp_clear_flush_notify(vma, haddr, pmd);
+	/*
+	 * leave pmd empty until pte is filled.
+	 */
+	pmdp_splitting_flush_notify(vma, haddr, pmd);
 
 	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
 	pmd_populate(mm, &_pmd, pgtable);
diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c
index 2fe699cedd4d..0fc1f5a06979 100644
--- a/mm/pgtable-generic.c
+++ b/mm/pgtable-generic.c
@@ -7,6 +7,7 @@
  */
 
 #include <linux/pagemap.h>
+#include <linux/mmu_notifier.h>
 #include <asm/tlb.h>
 #include <asm-generic/pgtable.h>
 
@@ -184,3 +185,13 @@ void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
+
+#ifndef __HAVE_ARCH_PMDP_SPLITTING_FLUSH_NOTIFY
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+void pmdp_splitting_flush_notify(struct vm_area_struct *vma,
+				 unsigned long address, pmd_t *pmdp)
+{
+	pmdp_clear_flush_notify(vma, address, pmdp);
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+#endif
-- 
2.1.4