mm: swap: update get_swap_pages() to take folio order

We are about to allow swap storage of any mTHP size.  To prepare for that,
let's change get_swap_pages() to take a folio order parameter instead of
nr_pages.  This makes the interface self-documenting; a power-of-2 number
of pages must be provided.  We will also need the order internally so this
simplifies accessing it.

Link: https://lkml.kernel.org/r/20240408183946.2991168-5-ryan.roberts@arm.comSigned-off-by: Ryan Roberts <ryan.roberts@arm.com>
Reviewed-by: "Huang, Ying" <ying.huang@intel.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Barry Song <21cnbao@gmail.com>
Cc: Barry Song <v-songbaohua@oppo.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Gao Xiang <xiang@kernel.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/swap.h

@@ -468,7 +468,7 @@ swp_entry_t folio_alloc_swap(struct folio *folio);
 bool folio_free_swap(struct folio *folio);
 void put_swap_folio(struct folio *folio, swp_entry_t entry);
 extern swp_entry_t get_swap_page_of_type(int);
-extern int get_swap_pages(int n, swp_entry_t swp_entries[], int entry_size);
+extern int get_swap_pages(int n, swp_entry_t swp_entries[], int order);
 extern int add_swap_count_continuation(swp_entry_t, gfp_t);
 extern void swap_shmem_alloc(swp_entry_t);
 extern int swap_duplicate(swp_entry_t);

mm/swap_slots.c

@@ -264,7 +264,7 @@ static int refill_swap_slots_cache(struct swap_slots_cache *cache)
 	cache->cur = 0;
 	if (swap_slot_cache_active)
 		cache->nr = get_swap_pages(SWAP_SLOTS_CACHE_SIZE,
-					   cache->slots, 1);
+					   cache->slots, 0);
 
 	return cache->nr;
 }
@@ -311,7 +311,7 @@ swp_entry_t folio_alloc_swap(struct folio *folio)
 
 	if (folio_test_large(folio)) {
 		if (IS_ENABLED(CONFIG_THP_SWAP))
-			get_swap_pages(1, &entry, folio_nr_pages(folio));
+			get_swap_pages(1, &entry, folio_order(folio));
 		goto out;
 	}
 
@@ -343,7 +343,7 @@ swp_entry_t folio_alloc_swap(struct folio *folio)
 			goto out;
 	}
 
-	get_swap_pages(1, &entry, 1);
+	get_swap_pages(1, &entry, 0);
 out:
 	if (mem_cgroup_try_charge_swap(folio, entry)) {
 		put_swap_folio(folio, entry);

mm/swapfile.c

@@ -278,15 +278,15 @@ static void discard_swap_cluster(struct swap_info_struct *si,
 #ifdef CONFIG_THP_SWAP
 #define SWAPFILE_CLUSTER	HPAGE_PMD_NR
 
-#define swap_entry_size(size)	(size)
+#define swap_entry_order(order)	(order)
 #else
 #define SWAPFILE_CLUSTER	256
 
 /*
- * Define swap_entry_size() as constant to let compiler to optimize
+ * Define swap_entry_order() as constant to let compiler to optimize
  * out some code if !CONFIG_THP_SWAP
  */
-#define swap_entry_size(size)	1
+#define swap_entry_order(order)	0
 #endif
 #define LATENCY_LIMIT		256
 
@@ -1042,9 +1042,10 @@ static void swap_free_cluster(struct swap_info_struct *si, unsigned long idx)
 	swap_range_free(si, offset, SWAPFILE_CLUSTER);
 }
 
-int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_size)
+int get_swap_pages(int n_goal, swp_entry_t swp_entries[], int entry_order)
 {
-	unsigned long size = swap_entry_size(entry_size);
+	int order = swap_entry_order(entry_order);
+	unsigned long size = 1 << order;
 	struct swap_info_struct *si, *next;
 	long avail_pgs;
 	int n_ret = 0;
@@ -1349,7 +1350,7 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
 	unsigned char *map;
 	unsigned int i, free_entries = 0;
 	unsigned char val;
-	int size = swap_entry_size(folio_nr_pages(folio));
+	int size = 1 << swap_entry_order(folio_order(folio));
 
 	si = _swap_info_get(entry);
 	if (!si)