[PATCH RFC 02/11] mm/migrate: handle retries in migrate_folios_move()

[Shivank Garg]

After extracting the unmap phase, migrate_pages_batch() still drives the
retry loop for the move phase and passes its retry bookkeeping to
migrate_folios_move(). This splits the move phase across the two
functions and requires several output parameters.

Move the retry loop and its bookkeeping into migrate_folios_move().
The function now takes the number of passes and reports failures through
@nr_failed, matching migrate_folios_unmap().

No functional change is intended.

Signed-off-by: Shivank Garg <shivankg@xxxxxxx>
---
 mm/migrate.c | 104 ++++++++++++++++++++++++++++-------------------------------
 1 file changed, 49 insertions(+), 55 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index 14a0f84009c6..89207bf515b9 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1729,51 +1729,61 @@ static void migrate_folios_move(struct list_head *src_folios,
 		free_folio_t put_new_folio, unsigned long private,
 		enum migrate_mode mode, enum migrate_reason reason,
 		struct list_head *ret_folios,
-		struct migrate_pages_stats *stats,
-		int *retry, int *thp_retry, int *nr_failed,
-		int *nr_retry_pages)
+		struct migrate_pages_stats *stats, int nr_pass,
+		int *nr_failed)
 {
 	struct folio *folio, *folio2, *dst, *dst2;
+	int retry = 1;
+	int thp_retry = 0;
+	int nr_retry_pages = 0;
 	bool is_thp;
 	int nr_pages;
-	int rc;
+	int pass, rc;
 
-	dst = list_first_entry(dst_folios, struct folio, lru);
-	dst2 = list_next_entry(dst, lru);
-	list_for_each_entry_safe(folio, folio2, src_folios, lru) {
-		is_thp = folio_test_large(folio) && folio_test_pmd_mappable(folio);
-		nr_pages = folio_nr_pages(folio);
+	for (pass = 0; pass < nr_pass && retry; pass++) {
+		retry = 0;
+		thp_retry = 0;
+		nr_retry_pages = 0;
 
-		cond_resched();
+		dst = list_first_entry(dst_folios, struct folio, lru);
+		dst2 = list_next_entry(dst, lru);
+		list_for_each_entry_safe(folio, folio2, src_folios, lru) {
+			is_thp = folio_test_large(folio) && folio_test_pmd_mappable(folio);
+			nr_pages = folio_nr_pages(folio);
 
-		rc = migrate_folio_move(put_new_folio, private,
-				folio, dst, mode,
-				reason, ret_folios);
-		/*
-		 * The rules are:
-		 *	0: folio will be freed
-		 *	-EAGAIN: stay on the src_folios list
-		 *	Other errno: put on ret_folios list
-		 */
-		switch (rc) {
-		case -EAGAIN:
-			*retry += 1;
-			*thp_retry += is_thp;
-			*nr_retry_pages += nr_pages;
-			break;
-		case 0:
-			stats->nr_succeeded += nr_pages;
-			stats->nr_thp_succeeded += is_thp;
-			break;
-		default:
-			*nr_failed += 1;
-			stats->nr_thp_failed += is_thp;
-			stats->nr_failed_pages += nr_pages;
-			break;
+			cond_resched();
+
+			rc = migrate_folio_move(put_new_folio, private,
+					folio, dst, mode, reason, ret_folios);
+			/*
+			 * The rules are:
+			 *	0: folio will be freed
+			 *	-EAGAIN: stay on the src_folios list
+			 *	Other errno: put on ret_folios list
+			 */
+			switch (rc) {
+			case -EAGAIN:
+				retry++;
+				thp_retry += is_thp;
+				nr_retry_pages += nr_pages;
+				break;
+			case 0:
+				stats->nr_succeeded += nr_pages;
+				stats->nr_thp_succeeded += is_thp;
+				break;
+			default:
+				*nr_failed += 1;
+				stats->nr_thp_failed += is_thp;
+				stats->nr_failed_pages += nr_pages;
+				break;
+			}
+			dst = dst2;
+			dst2 = list_next_entry(dst, lru);
 		}
-		dst = dst2;
-		dst2 = list_next_entry(dst, lru);
 	}
+	*nr_failed += retry;
+	stats->nr_thp_failed += thp_retry;
+	stats->nr_failed_pages += nr_retry_pages;
 }
 
 static void migrate_folios_undo(struct list_head *src_folios,
@@ -2000,11 +2010,7 @@ static int migrate_pages_batch(struct list_head *from,
 		struct list_head *ret_folios, struct list_head *split_folios,
 		struct migrate_pages_stats *stats, int nr_pass)
 {
-	int retry = 1;
-	int thp_retry = 1;
 	int nr_failed = 0;
-	int nr_retry_pages = 0;
-	int pass = 0;
 	int rc, rc_saved;
 	LIST_HEAD(unmap_folios);
 	LIST_HEAD(dst_folios);
@@ -2024,21 +2030,9 @@ static int migrate_pages_batch(struct list_head *from,
 	/* Flush TLBs for all unmapped folios */
 	try_to_unmap_flush();
 
-	retry = 1;
-	for (pass = 0; pass < nr_pass && retry; pass++) {
-		retry = 0;
-		thp_retry = 0;
-		nr_retry_pages = 0;
-
-		/* Move the unmapped folios */
-		migrate_folios_move(&unmap_folios, &dst_folios,
-				put_new_folio, private, mode, reason,
-				ret_folios, stats, &retry, &thp_retry,
-				&nr_failed, &nr_retry_pages);
-	}
-	nr_failed += retry;
-	stats->nr_thp_failed += thp_retry;
-	stats->nr_failed_pages += nr_retry_pages;
+	/* Move the unmapped folios */
+	migrate_folios_move(&unmap_folios, &dst_folios, put_new_folio, private,
+			mode, reason, ret_folios, stats, nr_pass, &nr_failed);
 
 	rc = rc_saved ? : nr_failed;
 out:

-- 
2.43.0