[PATCH] mm: swap: allocate folio only first time in __read_swap_cache_async()

Zhaoyu Liu
2024-07-31T13:18:50Z

It should be checked by filemap_get_folio() if SWAP_HAS_CACHE was
marked while reading a share swap page. It would re-allocate a folio
if the swap cache was not ready now. We save the new folio to avoid
page allocating again.

Signed-off-by: Zhaoyu Liu <liuzhaoyu.zackary@bytedance.com>
---
mm/swap_state.c | 58 ++++++++++++++++++++++++++-----------------------
1 file changed, 31 insertions(+), 27 deletions(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index a1726e49a5eb..65370d148175 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -435,6 +435,8 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
{
struct swap_info_struct *si;
struct folio *folio;
+ struct folio *new_folio = NULL;
+ struct folio *result = NULL;
void *shadow = NULL;

*new_page_allocated = false;
@@ -463,16 +465,19 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
* else swap_off will be aborted if we return NULL.
*/
if (!swap_swapcount(si, entry) && swap_slot_cache_enabled)
- goto fail_put_swap;
+ goto put_and_return;

/*
- * Get a new folio to read into from swap. Allocate it now,
- * before marking swap_map SWAP_HAS_CACHE, when -EEXIST will
- * cause any racers to loop around until we add it to cache.
+ * Get a new folio to read into from swap. Allocate it now if
+ * new_folio not exist, before marking swap_map SWAP_HAS_CACHE,
+ * when -EEXIST will cause any racers to loop around until we
+ * add it to cache.
*/
- folio = folio_alloc_mpol(gfp_mask, 0, mpol, ilx, numa_node_id());
- if (!folio)
- goto fail_put_swap;
+ if (!new_folio) {
+ new_folio = folio_alloc_mpol(gfp_mask, 0, mpol, ilx, numa_node_id());
+ if (!new_folio)
+ goto put_and_return;
+ }

/*
* Swap entry may have been freed since our caller observed it.
@@ -480,10 +485,8 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
err = swapcache_prepare(entry);
if (!err)
break;
-
- folio_put(folio);
- if (err != -EEXIST)
- goto fail_put_swap;
+ else if (err != -EEXIST)
+ goto put_and_return;

/*
* Protect against a recursive call to __read_swap_cache_async()
@@ -494,7 +497,7 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
* __read_swap_cache_async() in the writeback path.
*/
if (skip_if_exists)
- goto fail_put_swap;
+ goto put_and_return;

/*
* We might race against __delete_from_swap_cache(), and
@@ -509,36 +512,37 @@ struct folio *__read_swap_cache_async(swp_entry_t entry, gfp_t gfp_mask,
/*
* The swap entry is ours to swap in. Prepare the new folio.
*/
+ __folio_set_locked(new_folio);
+ __folio_set_swapbacked(new_folio);

- __folio_set_locked(folio);
- __folio_set_swapbacked(folio);
-
- if (mem_cgroup_swapin_charge_folio(folio, NULL, gfp_mask, entry))
+ if (mem_cgroup_swapin_charge_folio(new_folio, NULL, gfp_mask, entry))
goto fail_unlock;

/* May fail (-ENOMEM) if XArray node allocation failed. */
- if (add_to_swap_cache(folio, entry, gfp_mask & GFP_RECLAIM_MASK, &shadow))
+ if (add_to_swap_cache(new_folio, entry, gfp_mask & GFP_RECLAIM_MASK, &shadow))
goto fail_unlock;

mem_cgroup_swapin_uncharge_swap(entry);

if (shadow)
- workingset_refault(folio, shadow);
+ workingset_refault(new_folio, shadow);

- /* Caller will initiate read into locked folio */
- folio_add_lru(folio);
+ /* Caller will initiate read into locked new_folio */
+ folio_add_lru(new_folio);
*new_page_allocated = true;
+ folio = new_folio;
got_folio:
- put_swap_device(si);
- return folio;
+ result = folio;
+ goto put_and_return;

fail_unlock:
- put_swap_folio(folio, entry);
- folio_unlock(folio);
- folio_put(folio);
-fail_put_swap:
+ put_swap_folio(new_folio, entry);
+ folio_unlock(new_folio);
+put_and_return:
put_swap_device(si);
- return NULL;
+ if (!(*new_page_allocated) && new_folio)
+ folio_put(new_folio);
+ return result;
}

/*
--
2.25.1