[RFC PATCH 4/8] mm: shmem: support large folio allocation for shmem_replace_folio()

[Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>]

To support large folio swapin for shmem in the following patches, add
large folio allocation for the new replacement folio in shmem_replace_folio(),
as well as updating statistics using the number of pages in the folio.

Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
 mm/shmem.c | 13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index daab124c3e61..74821a7031b8 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1901,8 +1901,7 @@ static int shmem_replace_folio(struct folio **foliop, gfp_t gfp,
 	 * limit chance of success by further cpuset and node constraints.
 	 */
 	gfp &= ~GFP_CONSTRAINT_MASK;
-	VM_BUG_ON_FOLIO(folio_test_large(old), old);
-	new = shmem_alloc_folio(gfp, info, index);
+	new = shmem_alloc_hugefolio(gfp, info, index, folio_order(old));
 	if (!new)
 		return -ENOMEM;
 
@@ -1923,11 +1922,13 @@ static int shmem_replace_folio(struct folio **foliop, gfp_t gfp,
 	xa_lock_irq(&swap_mapping->i_pages);
 	error = shmem_replace_entry(swap_mapping, swap_index, old, new);
 	if (!error) {
+		int nr_pages = folio_nr_pages(old);
+
 		mem_cgroup_migrate(old, new);
-		__lruvec_stat_mod_folio(new, NR_FILE_PAGES, 1);
-		__lruvec_stat_mod_folio(new, NR_SHMEM, 1);
-		__lruvec_stat_mod_folio(old, NR_FILE_PAGES, -1);
-		__lruvec_stat_mod_folio(old, NR_SHMEM, -1);
+		__lruvec_stat_mod_folio(new, NR_FILE_PAGES, nr_pages);
+		__lruvec_stat_mod_folio(new, NR_SHMEM, nr_pages);
+		__lruvec_stat_mod_folio(old, NR_FILE_PAGES, -nr_pages);
+		__lruvec_stat_mod_folio(old, NR_SHMEM, -nr_pages);
 	}
 	xa_unlock_irq(&swap_mapping->i_pages);
 
-- 
2.39.3