mm, swap: add folio to swap cache directly on allocation

The allocator uses SWAP_HAS_CACHE to pin a swap slot upon allocation. 
SWAP_HAS_CACHE is being deprecated as it caused a lot of confusion.  This
pinning usage here can be dropped by adding the folio to swap cache
directly on allocation.

All swap allocations are folio-based now (except for hibernation), so the
swap allocator can always take the folio as the parameter.  And now both
swap cache (swap table) and swap map are protected by the cluster lock,
scanning the map and inserting the folio can be done in the same critical
section.  This eliminates the time window that a slot is pinned by
SWAP_HAS_CACHE, but it has no cache, and avoids touching the lock multiple
times.

This is both a cleanup and an optimization.

Link: https://lkml.kernel.org/r/20251220-swap-table-p2-v5-15-8862a265a033@tencent.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Reviewed-by: Baoquan He <bhe@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Cc: Yosry Ahmed <yosry.ahmed@linux.dev>
Cc: Deepanshu Kartikey <kartikey406@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Kairui Song <ryncsn@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 0 insertions, 5 deletions

diff --git a/include/linux/swap.h b/include/linux/swap.h
index aaa868f60b9c..517d24e96d8c 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -452,7 +452,6 @@ static inline long get_nr_swap_pages(void)
 }
 
 extern void si_swapinfo(struct sysinfo *);
-void put_swap_folio(struct folio *folio, swp_entry_t entry);
 extern int add_swap_count_continuation(swp_entry_t, gfp_t);
 int swap_type_of(dev_t device, sector_t offset);
 int find_first_swap(dev_t *device);
@@ -533,10 +532,6 @@ static inline void swap_put_entries_direct(swp_entry_t ent, int nr)
 {
 }
 
-static inline void put_swap_folio(struct folio *folio, swp_entry_t swp)
-{
-}
-
 static inline int __swap_count(swp_entry_t entry)
 {
 	return 0;