[PATCH v2] mm/migrate: correct nr_failed in migrate_pages_sync()
From: Zi Yan
Date: Mon Oct 16 2023 - 11:42:16 EST
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>
---
include/trace/events/migrate.h | 24 ++++++++++++++----------
mm/migrate.c | 15 +++++++++++----
2 files changed, 25 insertions(+), 14 deletions(-)
diff --git a/include/trace/events/migrate.h b/include/trace/events/migrate.h
index 061b5128f335..0190ef725b43 100644
--- a/include/trace/events/migrate.h
+++ b/include/trace/events/migrate.h
@@ -49,10 +49,11 @@ TRACE_EVENT(mm_migrate_pages,
TP_PROTO(unsigned long succeeded, unsigned long failed,
unsigned long thp_succeeded, unsigned long thp_failed,
- unsigned long thp_split, enum migrate_mode mode, int reason),
+ unsigned long thp_split, unsigned long large_folio_split,
+ enum migrate_mode mode, int reason),
TP_ARGS(succeeded, failed, thp_succeeded, thp_failed,
- thp_split, mode, reason),
+ thp_split, large_folio_split, mode, reason),
TP_STRUCT__entry(
__field( unsigned long, succeeded)
@@ -60,26 +61,29 @@ TRACE_EVENT(mm_migrate_pages,
__field( unsigned long, thp_succeeded)
__field( unsigned long, thp_failed)
__field( unsigned long, thp_split)
+ __field( unsigned long, large_folio_split)
__field( enum migrate_mode, mode)
__field( int, reason)
),
TP_fast_assign(
- __entry->succeeded = succeeded;
- __entry->failed = failed;
- __entry->thp_succeeded = thp_succeeded;
- __entry->thp_failed = thp_failed;
- __entry->thp_split = thp_split;
- __entry->mode = mode;
- __entry->reason = reason;
+ __entry->succeeded = succeeded;
+ __entry->failed = failed;
+ __entry->thp_succeeded = thp_succeeded;
+ __entry->thp_failed = thp_failed;
+ __entry->thp_split = thp_split;
+ __entry->large_folio_split = large_folio_split;
+ __entry->mode = mode;
+ __entry->reason = reason;
),
- TP_printk("nr_succeeded=%lu nr_failed=%lu nr_thp_succeeded=%lu nr_thp_failed=%lu nr_thp_split=%lu mode=%s reason=%s",
+ TP_printk("nr_succeeded=%lu nr_failed=%lu nr_thp_succeeded=%lu nr_thp_failed=%lu nr_thp_split=%lu nr_split=%lu mode=%s reason=%s",
__entry->succeeded,
__entry->failed,
__entry->thp_succeeded,
__entry->thp_failed,
__entry->thp_split,
+ __entry->large_folio_split,
__print_symbolic(__entry->mode, MIGRATE_MODE),
__print_symbolic(__entry->reason, MIGRATE_REASON))
);
diff --git a/mm/migrate.c b/mm/migrate.c
index c602bf6dec97..4caf405b6504 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++;
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 +1840,7 @@ 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;
+ nr_failed += astats.nr_split + astats.nr_thp_split;
/*
* Fall back to migrate all failed folios one by one synchronously. All
* failed folios except split THPs will be retried, so their failure
@@ -1969,7 +1975,8 @@ int migrate_pages(struct list_head *from, new_folio_t get_new_folio,
count_vm_events(THP_MIGRATION_SPLIT, stats.nr_thp_split);
trace_mm_migrate_pages(stats.nr_succeeded, stats.nr_failed_pages,
stats.nr_thp_succeeded, stats.nr_thp_failed,
- stats.nr_thp_split, mode, reason);
+ stats.nr_thp_split, stats.nr_split, mode,
+ reason);
if (ret_succeeded)
*ret_succeeded = stats.nr_succeeded;
--
2.42.0