mm: filemap: use xa_get_order() to get the swap entry order

In the following patches, shmem will support the swap out of large folios,
which means the shmem mappings may contain large order swap entries, so
using xa_get_order() to get the folio order of the shmem swap entry to
update the '*start' correctly.

[[email protected]: use xa_get_order() to get the swap entry order]
  Link: https://lkml.kernel.org/r/[email protected]
Link: https://lkml.kernel.org/r/6876d55145c1cc80e79df7884aa3a62e397b101d.1723434324.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <[email protected]>
Signed-off-by: Hugh Dickins <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Chris Li <[email protected]>
Cc: Daniel Gomez <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: "Huang, Ying" <[email protected]>
Cc: Kefeng Wang <[email protected]>
Cc: Lance Yang <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Pankaj Raghav <[email protected]>
Cc: Ryan Roberts <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: Zi Yan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 27 insertions, 14 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index fcfec2a78a30..fdaa1e5e3078 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2046,17 +2046,20 @@ unsigned find_get_entries(struct address_space *mapping, pgoff_t *start,
 		if (!folio_batch_add(fbatch, folio))
 			break;
 	}
-	rcu_read_unlock();
 
 	if (folio_batch_count(fbatch)) {
-		unsigned long nr = 1;
+		unsigned long nr;
 		int idx = folio_batch_count(fbatch) - 1;
 
 		folio = fbatch->folios[idx];
 		if (!xa_is_value(folio))
 			nr = folio_nr_pages(folio);
-		*start = indices[idx] + nr;
+		else
+			nr = 1 << xa_get_order(&mapping->i_pages, indices[idx]);
+		*start = round_down(indices[idx] + nr, nr);
 	}
+	rcu_read_unlock();
+
 	return folio_batch_count(fbatch);
 }
 
@@ -2088,10 +2091,17 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t *start,
 
 	rcu_read_lock();
 	while ((folio = find_get_entry(&xas, end, XA_PRESENT))) {
+		unsigned long base;
+		unsigned long nr;
+
 		if (!xa_is_value(folio)) {
-			if (folio->index < *start)
+			nr = folio_nr_pages(folio);
+			base = folio->index;
+			/* Omit large folio which begins before the start */
+			if (base < *start)
 				goto put;
-			if (folio_next_index(folio) - 1 > end)
+			/* Omit large folio which extends beyond the end */
+			if (base + nr - 1 > end)
 				goto put;
 			if (!folio_trylock(folio))
 				goto put;
@@ -2100,7 +2110,19 @@ unsigned find_lock_entries(struct address_space *mapping, pgoff_t *start,
 				goto unlock;
 			VM_BUG_ON_FOLIO(!folio_contains(folio, xas.xa_index),
 					folio);
+		} else {
+			nr = 1 << xa_get_order(&mapping->i_pages, xas.xa_index);
+			base = xas.xa_index & ~(nr - 1);
+			/* Omit order>0 value which begins before the start */
+			if (base < *start)
+				continue;
+			/* Omit order>0 value which extends beyond the end */
+			if (base + nr - 1 > end)
+				break;
 		}
+
+		/* Update start now so that last update is correct on return */
+		*start = base + nr;
 		indices[fbatch->nr] = xas.xa_index;
 		if (!folio_batch_add(fbatch, folio))
 			break;
@@ -2112,15 +2134,6 @@ put:
 	}
 	rcu_read_unlock();
 
-	if (folio_batch_count(fbatch)) {
-		unsigned long nr = 1;
-		int idx = folio_batch_count(fbatch) - 1;
-
-		folio = fbatch->folios[idx];
-		if (!xa_is_value(folio))
-			nr = folio_nr_pages(folio);
-		*start = indices[idx] + nr;
-	}
 	return folio_batch_count(fbatch);
 }