During shmem_split_large_entry(), large swap entries are covering n slots
and an order-0 folio needs to be inserted. Instead of splitting all
n slots, only the 1 slot covered by the folio need to be split and the
remaining n-1 shadow entries can be retained with orders ranging from 0 to
n-1. This method only requires (n/XA_CHUNK_SHIFT) new xa_nodes instead of
(n % XA_CHUNK_SHIFT) * (n/XA_CHUNK_SHIFT) new xa_nodes, compared to the
original xas_split_alloc() + xas_split() one.
For example, to split an order-9 large swap entry (assuming XA_CHUNK_SHIFT
is 6), 1 xa_node is needed instead of 8.
xas_try_split_min_order() is used to reduce the number of calls to
xas_try_split() during split.
Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
mm/shmem.c | 43 ++++++++++++++++---------------------------
1 file changed, 16 insertions(+), 27 deletions(-)
diff --git a/mm/shmem.c b/mm/shmem.c
index 671f63063fd4..b35ba250c53d 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2162,14 +2162,14 @@ static int shmem_split_large_entry(struct inode *inode, pgoff_t index,
{
struct address_space *mapping = inode->i_mapping;
XA_STATE_ORDER(xas, &mapping->i_pages, index, 0);
- void *alloced_shadow = NULL;
- int alloced_order = 0, i;
+ int split_order = 0;
+ int i;
/* Convert user data gfp flags to xarray node gfp flags */
gfp &= GFP_RECLAIM_MASK;
for (;;) {
- int order = -1, split_order = 0;
+ int order = -1;
void *old = NULL;
xas_lock_irq(&xas);
@@ -2181,20 +2181,21 @@ static int shmem_split_large_entry(struct inode *inode, pgoff_t index,
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) {
- if (!alloced_order) {
- split_order = order;
- goto unlock;
+ int cur_order = order;
+
+ split_order = xas_try_split_min_order(cur_order);
+
+ while (cur_order > 0) {
+ xas_set_order(&xas, index, split_order);
+ xas_try_split(&xas, old, cur_order, GFP_NOWAIT);
+ if (xas_error(&xas))
+ goto unlock;
+ cur_order = split_order;
+ split_order =
+ xas_try_split_min_order(split_order);
}
- xas_split(&xas, old, order);
/*
* Re-set the swap entry after splitting, and the swap
@@ -2213,26 +2214,14 @@ static int shmem_split_large_entry(struct inode *inode, pgoff_t index,
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;
+ return split_order;
}
/*
--
2.47.2
