Now the swap device can only swap-in order 0 folio, even though a large
folio is swapped out. This requires us to split the large entry previously
saved in the shmem pagecache to support the swap in of small folios.
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
mm/shmem.c | 95 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 95 insertions(+)
diff --git a/mm/shmem.c b/mm/shmem.c
index eb030827f7fb..b4468076f0e9 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1990,6 +1990,82 @@ static void shmem_set_folio_swapin_error(struct inode *inode, pgoff_t index,
swap_free_nr(swap, nr_pages);
}
+static int shmem_split_large_entry(struct inode *inode, pgoff_t index,
+ swp_entry_t swap, int new_order, gfp_t gfp)
+{
+ struct address_space *mapping = inode->i_mapping;
+ XA_STATE_ORDER(xas, &mapping->i_pages, index, new_order);
+ void *alloced_shadow = NULL;
+ int alloced_order = 0, i;
+
+ for (;;) {
+ int order = -1, split_order = 0;
+ void *old = NULL;
+
+ xas_lock_irq(&xas);
+ old = xas_load(&xas);
+ if (!xa_is_value(old) || swp_to_radix_entry(swap) != old) {
+ xas_set_err(&xas, -EEXIST);
+ goto unlock;
+ }
+
+ if (order == -1)
+ order = xas_get_order(&xas);
+
+ /* Swap entry may have changed before we re-acquire the lock */
+ if (alloced_order &&
+ (old != alloced_shadow || order != alloced_order)) {
+ xas_destroy(&xas);
+ alloced_order = 0;
+ }
+
+ /* Try to split large swap entry in pagecache */
+ if (order > 0 && order > new_order) {
+ if (!alloced_order) {
+ split_order = order;
+ goto unlock;
+ }
+ xas_split(&xas, old, order);
+
+ /*
+ * Re-set the swap entry after splitting, and the swap
+ * offset of the original large entry must be continuous.
+ */
+ for (i = 0; i < 1 << order; i += (1 << new_order)) {
+ pgoff_t aligned_index = round_down(index, 1 << order);
+ swp_entry_t tmp;
+
+ tmp = swp_entry(swp_type(swap), swp_offset(swap) + i);
+ __xa_store(&mapping->i_pages, aligned_index + i,
+ swp_to_radix_entry(tmp), 0);
+ }
+ }
+
+unlock:
+ xas_unlock_irq(&xas);
+
+ /* split needed, alloc here and retry. */
+ if (split_order) {
+ xas_split_alloc(&xas, old, split_order, gfp);
+ if (xas_error(&xas))
+ goto error;
+ alloced_shadow = old;
+ alloced_order = split_order;
+ xas_reset(&xas);
+ continue;
+ }
+
+ if (!xas_nomem(&xas, gfp))
+ break;
+ }
+
+error:
+ if (xas_error(&xas))
+ return xas_error(&xas);
+
+ return alloced_order;
+}
+
/*
* Swap in the folio pointed to by *foliop.
* Caller has to make sure that *foliop contains a valid swapped folio.
@@ -2026,12 +2102,31 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
/* Look it up and read it in.. */
folio = swap_cache_get_folio(swap, NULL, 0);
if (!folio) {
+ int split_order, offset;
+
/* Or update major stats only when swapin succeeds?? */
if (fault_type) {
*fault_type |= VM_FAULT_MAJOR;
count_vm_event(PGMAJFAULT);
count_memcg_event_mm(fault_mm, PGMAJFAULT);
}
+
+ /*
+ * Now swap device can only swap in order 0 folio, then we
+ * should split the large swap entry stored in the pagecache
+ * if necessary.
+ */
+ split_order = shmem_split_large_entry(inode, index, swap, 0, gfp);
+ if (split_order < 0) {
+ error = split_order;
+ goto failed;
+ }
+
+ if (split_order > 0) {
+ offset = index - round_down(index, 1 << split_order);
+ swap = swp_entry(swp_type(swap), swp_offset(swap) + offset);
+ }
+
/* Here we actually start the io */
folio = shmem_swapin_cluster(swap, gfp, info, index);
if (!folio) {
--
2.39.3
