[PATCH 3/9] mm: Convert unuse_pte() to use a folio throughout

["Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>]

Saves about eight calls to compound_head().

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 mm/swapfile.c | 47 +++++++++++++++++++++++++----------------------
 1 file changed, 25 insertions(+), 22 deletions(-)

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 88842c6fb8fe..21eced2d1f80 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1741,21 +1741,25 @@ static inline int pte_same_as_swp(pte_t pte, pte_t swp_pte)
 static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 		unsigned long addr, swp_entry_t entry, struct folio *folio)
 {
-	struct page *page = folio_file_page(folio, swp_offset(entry));
-	struct page *swapcache;
+	struct page *page;
+	struct folio *swapcache;
 	spinlock_t *ptl;
 	pte_t *pte, new_pte, old_pte;
-	bool hwpoisoned = PageHWPoison(page);
+	bool hwpoisoned = false;
 	int ret = 1;
 
-	swapcache = page;
+	swapcache = folio;
 	folio = ksm_might_need_to_copy(folio, vma, addr);
 	if (unlikely(!folio))
 		return -ENOMEM;
-	else if (unlikely(folio == ERR_PTR(-EHWPOISON)))
+	else if (unlikely(folio == ERR_PTR(-EHWPOISON))) {
+		hwpoisoned = true;
+		folio = swapcache;
+	}
+
+	page = folio_file_page(folio, swp_offset(entry));
+	if (PageHWPoison(page))
 		hwpoisoned = true;
-	else
-		page = folio_file_page(folio, swp_offset(entry));
 
 	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
 	if (unlikely(!pte || !pte_same_as_swp(ptep_get(pte),
@@ -1766,13 +1770,12 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 
 	old_pte = ptep_get(pte);
 
-	if (unlikely(hwpoisoned || !PageUptodate(page))) {
+	if (unlikely(hwpoisoned || !folio_test_uptodate(folio))) {
 		swp_entry_t swp_entry;
 
 		dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
 		if (hwpoisoned) {
-			swp_entry = make_hwpoison_entry(swapcache);
-			page = swapcache;
+			swp_entry = make_hwpoison_entry(page);
 		} else {
 			swp_entry = make_poisoned_swp_entry();
 		}
@@ -1786,7 +1789,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 	 * when reading from swap. This metadata may be indexed by swap entry
 	 * so this must be called before swap_free().
 	 */
-	arch_swap_restore(entry, page_folio(page));
+	arch_swap_restore(entry, folio);
 
 	/* See do_swap_page() */
 	VM_BUG_ON_FOLIO(!folio_test_anon(folio), folio);
@@ -1794,23 +1797,23 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 
 	dec_mm_counter(vma->vm_mm, MM_SWAPENTS);
 	inc_mm_counter(vma->vm_mm, MM_ANONPAGES);
-	get_page(page);
-	if (page == swapcache) {
+	folio_get(folio);
+	if (folio == swapcache) {
 		rmap_t rmap_flags = RMAP_NONE;
 
 		/*
-		 * See do_swap_page(): PageWriteback() would be problematic.
-		 * However, we do a wait_on_page_writeback() just before this
-		 * call and have the page locked.
+		 * See do_swap_page(): writeback would be problematic.
+		 * However, we do a folio_wait_writeback() just before this
+		 * call and have the folio locked.
 		 */
-		VM_BUG_ON_PAGE(PageWriteback(page), page);
+		VM_BUG_ON_FOLIO(folio_test_writeback(folio), folio);
 		if (pte_swp_exclusive(old_pte))
 			rmap_flags |= RMAP_EXCLUSIVE;
 
 		page_add_anon_rmap(page, vma, addr, rmap_flags);
 	} else { /* ksm created a completely new copy */
-		page_add_new_anon_rmap(page, vma, addr);
-		lru_cache_add_inactive_or_unevictable(page, vma);
+		folio_add_new_anon_rmap(folio, vma, addr);
+		folio_add_lru_vma(folio, vma);
 	}
 	new_pte = pte_mkold(mk_pte(page, vma->vm_page_prot));
 	if (pte_swp_soft_dirty(old_pte))
@@ -1823,9 +1826,9 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 out:
 	if (pte)
 		pte_unmap_unlock(pte, ptl);
-	if (page != swapcache) {
-		unlock_page(page);
-		put_page(page);
+	if (folio != swapcache) {
+		folio_unlock(folio);
+		folio_put(folio);
 	}
 	return ret;
 }
-- 
2.42.0