[PATCH v2 4/8] mm/khugepaged: factor out and simplify dirty/writeback handling

[Pedro Falcato <pfalcato@suse.de>]

Dirty/writeback folios can easily share most of the branch. These checks
are still gated under !is_shmem due to shmem not really having issues
with dirty folios.

While here, reflow the comment.

Signed-off-by: Pedro Falcato <pfalcato@suse.de>
---
 mm/khugepaged.c | 47 ++++++++++++++++++++++++-----------------------
 1 file changed, 24 insertions(+), 23 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index d5647a3ac095..0eee2b6bbe64 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2299,8 +2299,8 @@ prepare_collapse_file_folio(pgoff_t index, struct collapse_file_state *state)
 	struct address_space *mapping = state->mapping;
 	enum scan_result result = SCAN_SUCCEED;
 	const bool is_shmem = state->is_shmem;
+	bool dirty, new = false;
 	struct folio *folio;
-	bool new = false;
 
 	folio = maybe_read_folio(index, state, &new);
 	if (!folio)
@@ -2317,39 +2317,40 @@ prepare_collapse_file_folio(pgoff_t index, struct collapse_file_state *state)
 		goto xa_unlocked;
 	}
 
-	if (is_shmem) {
-		if (folio_trylock(folio)) {
-			folio_get(folio);
-		} else {
-			result = SCAN_PAGE_LOCK;
-			goto xa_locked;
-		}
-	} else {	/* !is_shmem */
-		if (folio_test_dirty(folio)) {
+	if (!is_shmem) {
+		dirty = folio_test_dirty(folio);
+		if (dirty || folio_test_writeback(folio)) {
 			/*
-			 * This page is dirty because it hasn't
-			 * been flushed since first write.
+			 * This folio is either dirty or under writeback.
+			 * khugepaged cannot operate on such folios.
 			 *
-			 * Trigger async flush for read-only files and
-			 * hope the writeback is done when khugepaged
-			 * revisits this page. Writable files can have
-			 * their folios dirty at any time; blindly
-			 * flushing them would cause undesirable
+			 * For dirty folios, trigger async flush for
+			 * read-only files and hope the writeback is done
+			 * when khugepaged revisits this page. Writable
+			 * files can have their folios dirty at any time;
+			 * blindly flushing them would cause undesirable
 			 * system-wide writeback.
 			 *
 			 * This is a one-off situation. We are not
 			 * forcing writeback in loop.
 			 */
 			xas_unlock_irq(state->xas);
-			if (!inode_is_open_for_write(mapping->host))
+			if (dirty && !inode_is_open_for_write(mapping->host))
 				filemap_flush(mapping);
 			result = SCAN_PAGE_DIRTY_OR_WRITEBACK;
 			goto xa_unlocked;
-		} else if (folio_test_writeback(folio)) {
-			xas_unlock_irq(state->xas);
-			result = SCAN_PAGE_DIRTY_OR_WRITEBACK;
-			goto xa_unlocked;
-		} else if (folio_trylock(folio)) {
+		}
+	}
+
+	if (is_shmem) {
+		if (folio_trylock(folio)) {
+			folio_get(folio);
+		} else {
+			result = SCAN_PAGE_LOCK;
+			goto xa_locked;
+		}
+	} else {	/* !is_shmem */
+		if (folio_trylock(folio)) {
 			folio_get(folio);
 		} else {
 			result = SCAN_PAGE_LOCK;
-- 
2.56.0