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-rw-r--r--mm/swapfile.c20
1 files changed, 12 insertions, 8 deletions
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 1b8c33907242..17bc224bce68 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1924,20 +1924,24 @@ static unsigned long read_swap_header(struct swap_info_struct *p,
/*
* Find out how many pages are allowed for a single swap
- * device. There are two limiting factors: 1) the number of
- * bits for the swap offset in the swp_entry_t type and
- * 2) the number of bits in the a swap pte as defined by
- * the different architectures. In order to find the
- * largest possible bit mask a swap entry with swap type 0
+ * device. There are three limiting factors: 1) the number
+ * of bits for the swap offset in the swp_entry_t type, and
+ * 2) the number of bits in the swap pte as defined by the
+ * the different architectures, and 3) the number of free bits
+ * in an exceptional radix_tree entry. In order to find the
+ * largest possible bit mask, a swap entry with swap type 0
* and swap offset ~0UL is created, encoded to a swap pte,
- * decoded to a swp_entry_t again and finally the swap
+ * decoded to a swp_entry_t again, and finally the swap
* offset is extracted. This will mask all the bits from
* the initial ~0UL mask that can't be encoded in either
* the swp_entry_t or the architecture definition of a
- * swap pte.
+ * swap pte. Then the same is done for a radix_tree entry.
*/
maxpages = swp_offset(pte_to_swp_entry(
- swp_entry_to_pte(swp_entry(0, ~0UL)))) + 1;
+ swp_entry_to_pte(swp_entry(0, ~0UL))));
+ maxpages = swp_offset(radix_to_swp_entry(
+ swp_to_radix_entry(swp_entry(0, maxpages)))) + 1;
+
if (maxpages > swap_header->info.last_page) {
maxpages = swap_header->info.last_page + 1;
/* p->max is an unsigned int: don't overflow it */