mm/ksm: use folio in write_protect_page

Compound page is checked and skipped before write_protect_page() called,
use folio to save a few compound_head checks.

Link: https://lkml.kernel.org/r/20240411061713.1847574-8-alexs@kernel.orgSigned-off-by: Alex Shi (tencent) <alexs@kernel.org>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/ksm.c

@@ -1289,23 +1289,24 @@ static u32 calc_checksum(struct page *page)
 	return checksum;
 }
 
-static int write_protect_page(struct vm_area_struct *vma, struct page *page,
+static int write_protect_page(struct vm_area_struct *vma, struct folio *folio,
 			      pte_t *orig_pte)
 {
 	struct mm_struct *mm = vma->vm_mm;
-	DEFINE_PAGE_VMA_WALK(pvmw, page, vma, 0, 0);
+	DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, 0, 0);
 	int swapped;
 	int err = -EFAULT;
 	struct mmu_notifier_range range;
 	bool anon_exclusive;
 	pte_t entry;
 
-	pvmw.address = page_address_in_vma(page, vma);
+	if (WARN_ON_ONCE(folio_test_large(folio)))
+		return err;
+
+	pvmw.address = page_address_in_vma(&folio->page, vma);
 	if (pvmw.address == -EFAULT)
 		goto out;
 
-	BUG_ON(PageTransCompound(page));
-
 	mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, pvmw.address,
 				pvmw.address + PAGE_SIZE);
 	mmu_notifier_invalidate_range_start(&range);
@@ -1315,12 +1316,12 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page,
 	if (WARN_ONCE(!pvmw.pte, "Unexpected PMD mapping?"))
 		goto out_unlock;
 
-	anon_exclusive = PageAnonExclusive(page);
+	anon_exclusive = PageAnonExclusive(&folio->page);
 	entry = ptep_get(pvmw.pte);
 	if (pte_write(entry) || pte_dirty(entry) ||
 	    anon_exclusive || mm_tlb_flush_pending(mm)) {
-		swapped = PageSwapCache(page);
-		flush_cache_page(vma, pvmw.address, page_to_pfn(page));
+		swapped = folio_test_swapcache(folio);
+		flush_cache_page(vma, pvmw.address, folio_pfn(folio));
 		/*
 		 * Ok this is tricky, when get_user_pages_fast() run it doesn't
 		 * take any lock, therefore the check that we are going to make
@@ -1340,20 +1341,20 @@ static int write_protect_page(struct vm_area_struct *vma, struct page *page,
 		 * Check that no O_DIRECT or similar I/O is in progress on the
 		 * page
 		 */
-		if (page_mapcount(page) + 1 + swapped != page_count(page)) {
+		if (folio_mapcount(folio) + 1 + swapped != folio_ref_count(folio)) {
 			set_pte_at(mm, pvmw.address, pvmw.pte, entry);
 			goto out_unlock;
 		}
 
 		/* See folio_try_share_anon_rmap_pte(): clear PTE first. */
 		if (anon_exclusive &&
-		    folio_try_share_anon_rmap_pte(page_folio(page), page)) {
+		    folio_try_share_anon_rmap_pte(folio, &folio->page)) {
 			set_pte_at(mm, pvmw.address, pvmw.pte, entry);
 			goto out_unlock;
 		}
 
 		if (pte_dirty(entry))
-			set_page_dirty(page);
+			folio_mark_dirty(folio);
 		entry = pte_mkclean(entry);
 
 		if (pte_write(entry))
@@ -1519,7 +1520,7 @@ static int try_to_merge_one_page(struct vm_area_struct *vma,
 	 * ptes are necessarily already write-protected.  But in either
 	 * case, we need to lock and check page_count is not raised.
 	 */
-	if (write_protect_page(vma, page, &orig_pte) == 0) {
+	if (write_protect_page(vma, page_folio(page), &orig_pte) == 0) {
 		if (!kpage) {
 			/*
 			 * While we hold page lock, upgrade page from