zswap: make zswap_store() take a folio

Patch series "Followup folio conversions for zswap".

With frontswap killed, it's worth converting the zswap_load() and
zswap_store() functions to take a folio instead of a page pointer.  They
aren't converted to support large folios, but there are a lot of
unnecessary calls to compound_head() that are removed by these patches.


This patch (of 4):

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.  This does remove a
few hidden calls to compound_head().

Link: https://lkml.kernel.org/r/20230715042343.434588-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20230715042343.434588-3-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: Matthew Wilcox (Oracle) <willy@infradead.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

@@ -10,7 +10,7 @@ extern atomic_t zswap_stored_pages;
 
 #ifdef CONFIG_ZSWAP
 
-bool zswap_store(struct page *page);
+bool zswap_store(struct folio *folio);
 bool zswap_load(struct page *page);
 void zswap_invalidate(int type, pgoff_t offset);
 void zswap_swapon(int type);
@@ -18,7 +18,7 @@ void zswap_swapoff(int type);
 
 #else
 
-static inline bool zswap_store(struct page *page)
+static inline bool zswap_store(struct folio *folio)
 {
 	return false;
 }

mm/page_io.c

@@ -195,7 +195,7 @@ int swap_writepage(struct page *page, struct writeback_control *wbc)
 		folio_unlock(folio);
 		return ret;
 	}
-	if (zswap_store(&folio->page)) {
+	if (zswap_store(folio)) {
 		folio_start_writeback(folio);
 		folio_unlock(folio);
 		folio_end_writeback(folio);

mm/zswap.c

@@ -1223,11 +1223,12 @@ static void zswap_fill_page(void *ptr, unsigned long value)
 	memset_l(page, value, PAGE_SIZE / sizeof(unsigned long));
 }
 
-bool zswap_store(struct page *page)
+bool zswap_store(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, *dupentry;
 	struct scatterlist input, output;
@@ -1242,11 +1243,11 @@ bool zswap_store(struct page *page)
 	gfp_t gfp;
 	int ret;
 
-	VM_WARN_ON_ONCE(!PageLocked(page));
-	VM_WARN_ON_ONCE(!PageSwapCache(page));
+	VM_WARN_ON_ONCE(!folio_test_locked(folio));
+	VM_WARN_ON_ONCE(!folio_test_swapcache(folio));
 
-	/* THP isn't supported */
-	if (PageTransHuge(page))
+	/* Large folios aren't supported */
+	if (folio_test_large(folio))
 		return false;
 
 	if (!zswap_enabled || !tree)