zswap: make zswap_load() take a folio

Only convert a few easy parts of this function to use the folio passed in;
convert back to struct page for the majority of it. Removes three hidden
calls to compound_head().

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Matthew Wilcox (Oracle) <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Domenico Cerasuolo <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Nhat Pham <[e-mail]>
Cc: Vitaly Wool <[e-mail]>
Cc: Yosry Ahmed <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/zswap.h

···
 #ifdef CONFIG_ZSWAP
 
 bool zswap_store(struct folio *folio);
-bool zswap_load(struct page *page);
+bool zswap_load(struct folio *folio);
 void zswap_invalidate(int type, pgoff_t offset);
 void zswap_swapon(int type);
 void zswap_swapoff(int type);
···
 	return false;
 }
 
-static inline bool zswap_load(struct page *page)
+static inline bool zswap_load(struct folio *folio)
 {
 	return false;
 }

mm/page_io.c

···
 	}
 	delayacct_swapin_start();
 
-	if (zswap_load(page)) {
+	if (zswap_load(folio)) {
 		folio_mark_uptodate(folio);
 		folio_unlock(folio);
 	} else if (data_race(sis->flags & SWP_FS_OPS)) {

mm/zswap.c

···
 	goto reject;
 }
 
-bool zswap_load(struct page *page)
+bool zswap_load(struct folio *folio)
 {
-	swp_entry_t swp = { .val = page_private(page), };
+	swp_entry_t swp = folio_swap_entry(folio);
 	int type = swp_type(swp);
 	pgoff_t offset = swp_offset(swp);
+	struct page *page = &folio->page;
 	struct zswap_tree *tree = zswap_trees[type];
 	struct zswap_entry *entry;
 	struct scatterlist input, output;
···
 	unsigned int dlen;
 	bool ret;
 
-	VM_WARN_ON_ONCE(!PageLocked(page));
+	VM_WARN_ON_ONCE(!folio_test_locked(folio));
 
 	/* find */
 	spin_lock(&tree->lock);
···
 	spin_lock(&tree->lock);
 	if (ret && zswap_exclusive_loads_enabled) {
 		zswap_invalidate_entry(tree, entry);
-		SetPageDirty(page);
+		folio_mark_dirty(folio);
 	} else if (entry->length) {
 		spin_lock(&entry->pool->lru_lock);
 		list_move(&entry->lru, &entry->pool->lru);