From: Zi Yan <ziy@xxxxxxxxxx>
nr_failed was missing the large folio splits from migrate_pages_batch()
and can cause a mismatch between migrate_pages() return value and the
number of not migrated pages, i.e., when the return value of
migrate_pages() is 0, there are still pages left in the from page list.
It will happen when a non-PMD THP large folio fails to migrate due to
-ENOMEM and is split successfully but not all the split pages are not
migrated, migrate_pages_batch() would return non-zero, but
astats.nr_thp_split = 0. nr_failed would be 0 and returned to the caller
of migrate_pages(), but the not migrated pages are left in the from page
list without being added back to LRU lists.
Fix it by adding a new nr_split counter for large folio splits and adding
it to nr_failed in migrate_page_sync() after migrate_pages_batch() is
done.
Fixes: 2ef7dbb26990 ("migrate_pages: try migrate in batch asynchronously firstly")
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
---
mm/migrate.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/mm/migrate.c b/mm/migrate.c
index c602bf6dec97..fc2e70b17704 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1495,6 +1495,7 @@ struct migrate_pages_stats {
int nr_thp_succeeded; /* THP migrated successfully */
int nr_thp_failed; /* THP failed to be migrated */
int nr_thp_split; /* THP split before migrating */
+ int nr_split; /* Large folio (include THP) split before migrating */
};
/*
@@ -1614,6 +1615,7 @@ static int migrate_pages_batch(struct list_head *from,
int nr_retry_pages = 0;
int pass = 0;
bool is_thp = false;
+ bool is_large = false;
struct folio *folio, *folio2, *dst = NULL, *dst2;
int rc, rc_saved = 0, nr_pages;
LIST_HEAD(unmap_folios);
@@ -1629,7 +1631,8 @@ static int migrate_pages_batch(struct list_head *from,
nr_retry_pages = 0;
list_for_each_entry_safe(folio, folio2, from, lru) {
- is_thp = folio_test_large(folio) && folio_test_pmd_mappable(folio);
+ is_large = folio_test_large(folio);
+ is_thp = is_large && folio_test_pmd_mappable(folio);
nr_pages = folio_nr_pages(folio);
cond_resched();
@@ -1649,6 +1652,7 @@ static int migrate_pages_batch(struct list_head *from,
stats->nr_thp_failed++;
if (!try_split_folio(folio, split_folios)) {
stats->nr_thp_split++;
+ stats->nr_split++;
continue;
}
stats->nr_failed_pages += nr_pages;
@@ -1677,11 +1681,12 @@ static int migrate_pages_batch(struct list_head *from,
nr_failed++;
stats->nr_thp_failed += is_thp;
/* Large folio NUMA faulting doesn't split to retry. */
- if (folio_test_large(folio) && !nosplit) {
+ if (is_large && !nosplit) {
int ret = try_split_folio(folio, split_folios);
if (!ret) {
stats->nr_thp_split += is_thp;
+ stats->nr_split += is_large;
break;
} else if (reason == MR_LONGTERM_PIN &&
ret == -EAGAIN) {
@@ -1827,6 +1832,7 @@ static int migrate_pages_sync(struct list_head *from, new_folio_t get_new_folio,
stats->nr_succeeded += astats.nr_succeeded;
stats->nr_thp_succeeded += astats.nr_thp_succeeded;
stats->nr_thp_split += astats.nr_thp_split;
+ stats->nr_split += astats.nr_split;
if (rc < 0) {
stats->nr_failed_pages += astats.nr_failed_pages;
stats->nr_thp_failed += astats.nr_thp_failed;
@@ -1834,7 +1840,11 @@ static int migrate_pages_sync(struct list_head *from, new_folio_t get_new_folio,
return rc;
}
stats->nr_thp_failed += astats.nr_thp_split;
- nr_failed += astats.nr_thp_split;
+ /*
+ * Do not count rc, as pages will be retried below.
+ * Count nr_split only, since it includes nr_thp_split.
+ */
+ nr_failed += astats.nr_split;
/*
* Fall back to migrate all failed folios one by one synchronously. All
* failed folios except split THPs will be retried, so their failure
--
2.42.0
