mm/damon/paddr: fix missing folio_put()

damon_get_folio() would always increase folio _refcount and
folio_isolate_lru() would increase folio _refcount if the folio's lru flag
is set.

If an unevictable folio isolated successfully, there will be two more
_refcount.  The one from folio_isolate_lru() will be decreased in
folio_puback_lru(), but the other one from damon_get_folio() will be left
behind.  This causes a pin page.

Whatever the case, the _refcount from damon_get_folio() should be
decreased.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 57223ac ("mm/damon/paddr: support the pageout scheme")
Signed-off-by: andrew.yang <[email protected]>
Reviewed-by: SeongJae Park <[email protected]>
Cc: <[email protected]>	[5.16.x]
Signed-off-by: Andrew Morton <[email protected]>

Author: QQXanadu

mm/damon/paddr.c

@@ -250,12 +250,11 @@ static unsigned long damon_pa_pageout(struct damon_region *r, struct damos *s)
 			folio_put(folio);
 			continue;
 		}
-		if (folio_test_unevictable(folio)) {
+		if (folio_test_unevictable(folio))
 			folio_putback_lru(folio);
-		} else {
+		else
 			list_add(&folio->lru, &folio_list);
-			folio_put(folio);
-		}
+		folio_put(folio);
 	}
 	applied = reclaim_pages(&folio_list);
 	cond_resched();