Migration is currently implemented as a mode of operation for
try_to_unmap_one() generally specified by passing the TTU_MIGRATION flag
or in the case of splitting a huge anonymous page TTU_SPLIT_FREEZE.

However it does not have much in common with the rest of the unmap
functionality of try_to_unmap_one() and thus splitting it into a
separate function reduces the complexity of try_to_unmap_one() making it
more readable.

Several simplifications can also be made in try_to_migrate_one() based
on the following observations:

 - All users of TTU_MIGRATION also set TTU_IGNORE_MLOCK.
 - No users of TTU_MIGRATION ever set TTU_IGNORE_HWPOISON.
 - No users of TTU_MIGRATION ever set TTU_BATCH_FLUSH.

TTU_SPLIT_FREEZE is a special case of migration used when splitting an
anonymous page. This is most easily dealt with by calling the correct
function from unmap_page() in mm/huge_memory.c  - either
try_to_migrate() for PageAnon or try_to_unmap().

Signed-off-by: Alistair Popple <apopple@nvidia.com>
---
 include/linux/rmap.h |   4 +-
 mm/huge_memory.c     |  10 +-
 mm/migrate.c         |   9 +-
 mm/rmap.c            | 352 +++++++++++++++++++++++++++++++------------
 4 files changed, 269 insertions(+), 106 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 7f1ee411bd7b..77fa17de51d7 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h

@@ -86,8 +86,6 @@ struct anon_vma_chain {
 };

 enum ttu_flags {
-	TTU_MIGRATION		= 0x1,	/* migration mode */
-
 	TTU_SPLIT_HUGE_PMD	= 0x4,	/* split huge PMD if any */

 	TTU_IGNORE_MLOCK	= 0x8,	/* ignore mlock */
 	TTU_IGNORE_HWPOISON	= 0x20,	/* corrupted page is recoverable */

@@ -96,7 +94,6 @@ enum ttu_flags {
 					 * do a final flush if necessary */
 	TTU_RMAP_LOCKED		= 0x80,	/* do not grab rmap lock:
 					 * caller holds it */
-	TTU_SPLIT_FREEZE	= 0x100,		/* freeze pte under splitting thp */
 };

 #ifdef CONFIG_MMU

@@ -193,6 +190,7 @@ static inline void page_dup_rmap(struct page *page, bool compound)
 int page_referenced(struct page *, int is_locked,
 			struct mem_cgroup *memcg, unsigned long *vm_flags);

+bool try_to_migrate(struct page *page, enum ttu_flags flags);
 bool try_to_unmap(struct page *, enum ttu_flags flags);

 /* Avoid racy checks */

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index d00b93dc2d9e..357052a4567b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c

@@ -2351,16 +2351,16 @@ void vma_adjust_trans_huge(struct vm_area_struct *vma,

 static void unmap_page(struct page *page)
 {
-	enum ttu_flags ttu_flags = TTU_IGNORE_MLOCK |
-		TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD;
+	enum ttu_flags ttu_flags = TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD;
 	bool unmap_success;

 	VM_BUG_ON_PAGE(!PageHead(page), page);

 	if (PageAnon(page))
-		ttu_flags |= TTU_SPLIT_FREEZE;
-
-	unmap_success = try_to_unmap(page, ttu_flags);
+		unmap_success = try_to_migrate(page, ttu_flags);
+	else
+		unmap_success = try_to_unmap(page, ttu_flags |
+						TTU_IGNORE_MLOCK);