mm/rmap: fix comments left over from recent changes

Parallel developments in mm/rmap.c have left behind some out-of-date
comments: try_to_migrate_one() also accepts TTU_SYNC (already commented
in try_to_migrate() itself), and try_to_migrate() returns nothing at
all.

TTU_SPLIT_FREEZE has just been deleted, so reword the comment about it
in mm/huge_memory.c; and TTU_IGNORE_ACCESS was removed in 5.11, so
delete the "recently referenced" comment from try_to_unmap_one() (once
upon a time the comment was near the removed codeblock, but they drifted
apart).

Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Link: https://lore.kernel.org/lkml/563ce5b2-7a44-5b4d-1dfd-59a0e65932a9@google.com/
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: Hugh Dickins

mm/huge_memory.c

@@ -2331,7 +2331,7 @@ static void remap_page(struct page *page, unsigned int nr)
 {
 	int i;
 
-	/* If TTU_SPLIT_FREEZE is ever extended to file, remove this check */
+	/* If unmap_page() uses try_to_migrate() on file, remove this check */
 	if (!PageAnon(page))
 		return;
 	if (PageTransHuge(page)) {

mm/rmap.c

@@ -1439,8 +1439,6 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 	while (page_vma_mapped_walk(&pvmw)) {
 		/*
 		 * If the page is mlock()d, we cannot swap it out.
-		 * If it's recently referenced (perhaps page_referenced
-		 * skipped over this mm) then we should reactivate it.
 		 */
 		if (!(flags & TTU_IGNORE_MLOCK)) {
 			if (vma->vm_flags & VM_LOCKED) {
@@ -1687,8 +1685,7 @@ void try_to_unmap(struct page *page, enum ttu_flags flags)
  * @arg: enum ttu_flags will be passed to this argument.
  *
  * If TTU_SPLIT_HUGE_PMD is specified any PMD mappings will be split into PTEs
- * containing migration entries. This and TTU_RMAP_LOCKED are the only supported
- * flags.
+ * containing migration entries.
  */
 static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
 		     unsigned long address, void *arg)
@@ -1928,8 +1925,6 @@ static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
  *
  * Tries to remove all the page table entries which are mapping this page and
  * replace them with special swap entries. Caller must hold the page lock.
- *
- * If is successful, return true. Otherwise, false.
  */
 void try_to_migrate(struct page *page, enum ttu_flags flags)
 {