mm/filemap: unify dropbehind flag testing and clearing

The read and write side does this a bit differently, unify it such that
the _{read,write} helpers check the bit before locking, and the generic
handler is in charge of clearing the bit and invalidating, once under
the folio lock.

Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/mm/filemap.c b/mm/filemap.c
index 2ba1ed116103abc8debf5fd9a157e67be868134c..eef44d7ea12e03b32fcf71d3196c61633369b3d7 100644 (file)
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1595,7 +1595,11 @@ static void filemap_end_dropbehind(struct folio *folio)
 
        VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
 
-       if (mapping && !folio_test_writeback(folio) && !folio_test_dirty(folio))
+       if (folio_test_writeback(folio) || folio_test_dirty(folio))
+               return;
+       if (!folio_test_clear_dropbehind(folio))
+               return;
+       if (mapping)
                folio_unmap_invalidate(mapping, folio, 0);
 }
 
@@ -1606,6 +1610,9 @@ static void filemap_end_dropbehind(struct folio *folio)
  */
 static void filemap_end_dropbehind_write(struct folio *folio)
 {
+       if (!folio_test_dropbehind(folio))
+               return;
+
        /*
         * Hitting !in_task() should not happen off RWF_DONTCACHE writeback,
         * but can happen if normal writeback just happens to find dirty folios
@@ -1629,8 +1636,6 @@ static void filemap_end_dropbehind_write(struct folio *folio)
  */
 void folio_end_writeback(struct folio *folio)
 {
-       bool folio_dropbehind = false;
-
        VM_BUG_ON_FOLIO(!folio_test_writeback(folio), folio);
 
        /*
@@ -1652,14 +1657,11 @@ void folio_end_writeback(struct folio *folio)
         * reused before the folio_wake_bit().
         */
        folio_get(folio);
-       if (!folio_test_dirty(folio))
-               folio_dropbehind = folio_test_clear_dropbehind(folio);
        if (__folio_end_writeback(folio))
                folio_wake_bit(folio, PG_writeback);
-       acct_reclaim_writeback(folio);
 
-       if (folio_dropbehind)
-               filemap_end_dropbehind_write(folio);
+       filemap_end_dropbehind_write(folio);
+       acct_reclaim_writeback(folio);
        folio_put(folio);
 }
 EXPORT_SYMBOL(folio_end_writeback);
@@ -2651,8 +2653,7 @@ static void filemap_end_dropbehind_read(struct folio *folio)
        if (folio_test_writeback(folio) || folio_test_dirty(folio))
                return;
        if (folio_trylock(folio)) {
-               if (folio_test_clear_dropbehind(folio))
-                       filemap_end_dropbehind(folio);
+               filemap_end_dropbehind(folio);
                folio_unlock(folio);
        }
 }