swap: turn get_swap_page() into folio_alloc_swap()

This removes an assumption that a large folio is HPAGE_PMD_NR pages
in size.

Link: https://lkml.kernel.org/r/20220504182857.4013401-8-willy@infradead.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 9 insertions, 8 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 9398e915b36b..bfa41bf5e190 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -77,9 +77,9 @@ static PLIST_HEAD(swap_active_head);
 /*
  * all available (active, not full) swap_info_structs
  * protected with swap_avail_lock, ordered by priority.
- * This is used by get_swap_page() instead of swap_active_head
+ * This is used by folio_alloc_swap() instead of swap_active_head
  * because swap_active_head includes all swap_info_structs,
- * but get_swap_page() doesn't need to look at full ones.
+ * but folio_alloc_swap() doesn't need to look at full ones.
  * This uses its own lock instead of swap_lock because when a
  * swap_info_struct changes between not-full/full, it needs to
  * add/remove itself to/from this list, but the swap_info_struct->lock
@@ -2109,11 +2109,12 @@ retry:
 	 * Under global memory pressure, swap entries can be reinserted back
 	 * into process space after the mmlist loop above passes over them.
 	 *
-	 * Limit the number of retries? No: when mmget_not_zero() above fails,
-	 * that mm is likely to be freeing swap from exit_mmap(), which proceeds
-	 * at its own independent pace; and even shmem_writepage() could have
-	 * been preempted after get_swap_page(), temporarily hiding that swap.
-	 * It's easy and robust (though cpu-intensive) just to keep retrying.
+	 * Limit the number of retries? No: when mmget_not_zero()
+	 * above fails, that mm is likely to be freeing swap from
+	 * exit_mmap(), which proceeds at its own independent pace;
+	 * and even shmem_writepage() could have been preempted after
+	 * folio_alloc_swap(), temporarily hiding that swap.  It's easy
+	 * and robust (though cpu-intensive) just to keep retrying.
 	 */
 	if (READ_ONCE(si->inuse_pages)) {
 		if (!signal_pending(current))
@@ -2327,7 +2328,7 @@ static void _enable_swap_info(struct swap_info_struct *p)
 	 * which on removal of any swap_info_struct with an auto-assigned
 	 * (i.e. negative) priority increments the auto-assigned priority
 	 * of any lower-priority swap_info_structs.
-	 * swap_avail_head needs to be priority ordered for get_swap_page(),
+	 * swap_avail_head needs to be priority ordered for folio_alloc_swap(),
 	 * which allocates swap pages from the highest available priority
 	 * swap_info_struct.
 	 */