The folio_migrate_mapping() function is splitted into two parts,
folio_refs_check_and_freeze() and folio_replace_mapping_and_unfreeze(),
also update comment from page to folio.
Note, the folio_ref_freeze() is moved out of xas_lock_irq(), since the
folio is already isolated and locked during migration, so suppose that
there is no functional change.
Signed-off-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
---
mm/migrate.c | 74 +++++++++++++++++++++++++++++-----------------------
1 file changed, 42 insertions(+), 32 deletions(-)
diff --git a/mm/migrate.c b/mm/migrate.c
index 6a9bb4af2595..b27c66af385d 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -419,50 +419,49 @@ static int folio_expected_refs(struct address_space *mapping,
}
/*
- * Replace the page in the mapping.
- *
* The number of remaining references must be:
- * 1 for anonymous pages without a mapping
- * 2 for pages with a mapping
- * 3 for pages with a mapping and PagePrivate/PagePrivate2 set.
+ * 1 for anonymous folios without a mapping
+ * 2 for folios with a mapping
+ * 3 for folios with a mapping and PagePrivate/PagePrivate2 set.
*/
-int folio_migrate_mapping(struct address_space *mapping,
- struct folio *newfolio, struct folio *folio, int extra_count)
+static int folio_refs_check_and_freeze(struct address_space *mapping,
+ struct folio *folio, int expected_cnt)
+{
+ if (!mapping) {
+ if (folio_ref_count(folio) != expected_cnt)
+ return -EAGAIN;
+ } else {
+ if (!folio_ref_freeze(folio, expected_cnt))
+ return -EAGAIN;
+ }
+
+ return 0;
+}
+
+/* The folio refcount must be freezed if folio with a mapping */
+static void folio_replace_mapping_and_unfreeze(struct address_space *mapping,
+ struct folio *newfolio, struct folio *folio, int expected_cnt)
{
XA_STATE(xas, &mapping->i_pages, folio_index(folio));
struct zone *oldzone, *newzone;
- int dirty;
- int expected_count = folio_expected_refs(mapping, folio) + extra_count;
long nr = folio_nr_pages(folio);
long entries, i;
+ int dirty;
if (!mapping) {
- /* Anonymous page without mapping */
- if (folio_ref_count(folio) != expected_count)
- return -EAGAIN;
-
- /* No turning back from here */
+ /* Anonymous folio without mapping */
newfolio->index = folio->index;
newfolio->mapping = folio->mapping;
if (folio_test_swapbacked(folio))
__folio_set_swapbacked(newfolio);
-
- return MIGRATEPAGE_SUCCESS;
+ return;
}
oldzone = folio_zone(folio);
newzone = folio_zone(newfolio);
+ /* Now we know that no one else is looking at the folio */
xas_lock_irq(&xas);
- if (!folio_ref_freeze(folio, expected_count)) {
- xas_unlock_irq(&xas);
- return -EAGAIN;
- }
-
- /*
- * Now we know that no one else is looking at the folio:
- * no turning back from here.
- */
newfolio->index = folio->index;
newfolio->mapping = folio->mapping;
folio_ref_add(newfolio, nr); /* add cache reference */
@@ -478,7 +477,7 @@ int folio_migrate_mapping(struct address_space *mapping,
entries = 1;
}
- /* Move dirty while page refs frozen and newpage not yet exposed */
+ /* Move dirty while folio refs frozen and newfolio not yet exposed */
dirty = folio_test_dirty(folio);
if (dirty) {
folio_clear_dirty(folio);
@@ -492,22 +491,22 @@ int folio_migrate_mapping(struct address_space *mapping,
}
/*
- * Drop cache reference from old page by unfreezing
- * to one less reference.
+ * Since old folio's refcount freezed, now drop cache reference from
+ * old folio by unfreezing to one less reference.
* We know this isn't the last reference.
*/
- folio_ref_unfreeze(folio, expected_count - nr);
+ folio_ref_unfreeze(folio, expected_cnt - nr);
xas_unlock(&xas);
/* Leave irq disabled to prevent preemption while updating stats */
/*
* If moved to a different zone then also account
- * the page for that zone. Other VM counters will be
+ * the folio for that zone. Other VM counters will be
* taken care of when we establish references to the
- * new page and drop references to the old page.
+ * new folio and drop references to the old folio.
*
- * Note that anonymous pages are accounted for
+ * Note that anonymous folios are accounted for
* via NR_FILE_PAGES and NR_ANON_MAPPED if they
* are mapped to swap space.
*/
@@ -544,7 +543,18 @@ int folio_migrate_mapping(struct address_space *mapping,
}
}
local_irq_enable();
+}
+
+int folio_migrate_mapping(struct address_space *mapping, struct folio *newfolio,
+ struct folio *folio, int extra_count)
+{
+ int ret, expected = folio_expected_refs(mapping, folio) + extra_count;
+
+ ret = folio_refs_check_and_freeze(mapping, folio, expected);
+ if (ret)
+ return ret;
+ folio_replace_mapping_and_unfreeze(mapping, newfolio, folio, expected);
return MIGRATEPAGE_SUCCESS;
}
EXPORT_SYMBOL(folio_migrate_mapping);
--
2.27.0
