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/20230715042343.434588-6-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Nhat Pham <nphamcs@gmail.com>
Cc: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/zswap.h

@@ -11,7 +11,7 @@ extern atomic_t zswap_stored_pages;
 #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);
@@ -23,7 +23,7 @@ static inline bool zswap_store(struct folio *folio)
 	return false;
 }
 
-static inline bool zswap_load(struct page *page)
+static inline bool zswap_load(struct folio *folio)
 {
 	return false;
 }

mm/page_io.c

@@ -513,7 +513,7 @@ void swap_readpage(struct page *page, bool synchronous, struct swap_iocb **plug)
 	}
 	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

@@ -1405,11 +1405,12 @@ bool zswap_store(struct folio *folio)
 	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;
@@ -1419,7 +1420,7 @@ bool zswap_load(struct page *page)
 	unsigned int dlen;
 	bool ret;
 
-	VM_WARN_ON_ONCE(!PageLocked(page));
+	VM_WARN_ON_ONCE(!folio_test_locked(folio));
 
 	/* find */
 	spin_lock(&tree->lock);
@@ -1481,7 +1482,7 @@ bool zswap_load(struct page *page)
 	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);