filemap: Add folio_put_wait_locked()

Convert all three callers of put_and_wait_on_page_locked() to
folio_put_wait_locked().  This shrinks the kernel overall by 19 bytes.
filemap_update_page() shrinks by 19 bytes while __migration_entry_wait()
is unchanged.  folio_put_wait_locked() is 14 bytes smaller than
put_and_wait_on_page_locked(), but pmd_migration_entry_wait() grows by
14 bytes.  It removes the assumption from pmd_migration_entry_wait()
that pages cannot be larger than a PMD (which is true today, but
may be interesting to explore in the future).

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>

include/linux/pagemap.h

@@ -868,7 +868,7 @@ static inline int wait_on_page_locked_killable(struct page *page)
 	return folio_wait_locked_killable(page_folio(page));
 }
 
-int put_and_wait_on_page_locked(struct page *page, int state);
+int folio_put_wait_locked(struct folio *folio, int state);
 void wait_on_page_writeback(struct page *page);
 void folio_wait_writeback(struct folio *folio);
 int folio_wait_writeback_killable(struct folio *folio);

mm/filemap.c

@@ -1259,10 +1259,10 @@ enum behavior {
 			 * __folio_lock() waiting on then setting PG_locked.
 			 */
 	SHARED,		/* Hold ref to page and check the bit when woken, like
-			 * wait_on_page_writeback() waiting on PG_writeback.
+			 * folio_wait_writeback() waiting on PG_writeback.
 			 */
 	DROP,		/* Drop ref to page before wait, no check when woken,
-			 * like put_and_wait_on_page_locked() on PG_locked.
+			 * like folio_put_wait_locked() on PG_locked.
 			 */
 };
 
@@ -1439,22 +1439,21 @@ int folio_wait_bit_killable(struct folio *folio, int bit_nr)
 EXPORT_SYMBOL(folio_wait_bit_killable);
 
 /**
- * put_and_wait_on_page_locked - Drop a reference and wait for it to be unlocked
- * @page: The page to wait for.
+ * folio_put_wait_locked - Drop a reference and wait for it to be unlocked
+ * @folio: The folio to wait for.
  * @state: The sleep state (TASK_KILLABLE, TASK_UNINTERRUPTIBLE, etc).
  *
- * The caller should hold a reference on @page.  They expect the page to
+ * The caller should hold a reference on @folio.  They expect the page to
  * become unlocked relatively soon, but do not wish to hold up migration
- * (for example) by holding the reference while waiting for the page to
+ * (for example) by holding the reference while waiting for the folio to
  * come unlocked.  After this function returns, the caller should not
- * dereference @page.
+ * dereference @folio.
  *
- * Return: 0 if the page was unlocked or -EINTR if interrupted by a signal.
+ * Return: 0 if the folio was unlocked or -EINTR if interrupted by a signal.
  */
-int put_and_wait_on_page_locked(struct page *page, int state)
+int folio_put_wait_locked(struct folio *folio, int state)
 {
-	return folio_wait_bit_common(page_folio(page), PG_locked, state,
-			DROP);
+	return folio_wait_bit_common(folio, PG_locked, state, DROP);
 }
 
 /**
@@ -2447,7 +2446,11 @@ static int filemap_update_page(struct kiocb *iocb,
 			goto unlock_mapping;
 		if (!(iocb->ki_flags & IOCB_WAITQ)) {
 			filemap_invalidate_unlock_shared(mapping);
-			put_and_wait_on_page_locked(&folio->page, TASK_KILLABLE);
+			/*
+			 * This is where we usually end up waiting for a
+			 * previously submitted readahead to finish.
+			 */
+			folio_put_wait_locked(folio, TASK_KILLABLE);
 			return AOP_TRUNCATED_PAGE;
 		}
 		error = __folio_lock_async(folio, iocb->ki_waitq);

mm/migrate.c

@@ -291,7 +291,7 @@ void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
 {
 	pte_t pte;
 	swp_entry_t entry;
-	struct page *page;
+	struct folio *folio;
 
 	spin_lock(ptl);
 	pte = *ptep;
@@ -302,18 +302,17 @@ void __migration_entry_wait(struct mm_struct *mm, pte_t *ptep,
 	if (!is_migration_entry(entry))
 		goto out;
 
-	page = pfn_swap_entry_to_page(entry);
-	page = compound_head(page);
+	folio = page_folio(pfn_swap_entry_to_page(entry));
 
 	/*
 	 * Once page cache replacement of page migration started, page_count
-	 * is zero; but we must not call put_and_wait_on_page_locked() without
-	 * a ref. Use get_page_unless_zero(), and just fault again if it fails.
+	 * is zero; but we must not call folio_put_wait_locked() without
+	 * a ref. Use folio_try_get(), and just fault again if it fails.
 	 */
-	if (!get_page_unless_zero(page))
+	if (!folio_try_get(folio))
 		goto out;
 	pte_unmap_unlock(ptep, ptl);
-	put_and_wait_on_page_locked(page, TASK_UNINTERRUPTIBLE);
+	folio_put_wait_locked(folio, TASK_UNINTERRUPTIBLE);
 	return;
 out:
 	pte_unmap_unlock(ptep, ptl);
@@ -338,16 +337,16 @@ void migration_entry_wait_huge(struct vm_area_struct *vma,
 void pmd_migration_entry_wait(struct mm_struct *mm, pmd_t *pmd)
 {
 	spinlock_t *ptl;
-	struct page *page;
+	struct folio *folio;
 
 	ptl = pmd_lock(mm, pmd);
 	if (!is_pmd_migration_entry(*pmd))
 		goto unlock;
-	page = pfn_swap_entry_to_page(pmd_to_swp_entry(*pmd));
-	if (!get_page_unless_zero(page))
+	folio = page_folio(pfn_swap_entry_to_page(pmd_to_swp_entry(*pmd)));
+	if (!folio_try_get(folio))
 		goto unlock;
 	spin_unlock(ptl);
-	put_and_wait_on_page_locked(page, TASK_UNINTERRUPTIBLE);
+	folio_put_wait_locked(folio, TASK_UNINTERRUPTIBLE);
 	return;
 unlock:
 	spin_unlock(ptl);