[PATCH 2/5] mm/khugepaged: Convert hpage_collapse_scan_pmd() to use folios

[Vishal Moola (Oracle)]

Replaces 5 calls to compound_head(), and removes 1466 bytes of kernel
text.

Previously, to determine if any pte was shared, the page mapcount
corresponding exactly to the pte was checked. This gave us a precise
number of shared ptes. Using folio_estimated_sharers() instead uses
the mapcount of the head page, giving us an estimate for tail page ptes.

This means if a tail page's mapcount is greater than its head page's
mapcount, folio_estimated_sharers() would be underestimating the number of
shared ptes, and vice versa.

Signed-off-by: Vishal Moola (Oracle) <vishal.moola@xxxxxxxxx>
---
 mm/khugepaged.c | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 7a552fe16c92..67aac53b31c8 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1245,7 +1245,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
 	pte_t *pte, *_pte;
 	int result = SCAN_FAIL, referenced = 0;
 	int none_or_zero = 0, shared = 0;
-	struct page *page = NULL;
+	struct folio *folio = NULL;
 	unsigned long _address;
 	spinlock_t *ptl;
 	int node = NUMA_NO_NODE, unmapped = 0;
@@ -1316,13 +1316,13 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
 		if (pte_write(pteval))
 			writable = true;
 
-		page = vm_normal_page(vma, _address, pteval);
-		if (unlikely(!page) || unlikely(is_zone_device_page(page))) {
+		folio = vm_normal_folio(vma, _address, pteval);
+		if (unlikely(!folio) || unlikely(folio_is_zone_device(folio))) {
 			result = SCAN_PAGE_NULL;
 			goto out_unmap;
 		}
 
-		if (page_mapcount(page) > 1) {
+		if (folio_estimated_sharers(folio) > 1) {
 			++shared;
 			if (cc->is_khugepaged &&
 			    shared > khugepaged_max_ptes_shared) {
@@ -1332,29 +1332,27 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
 			}
 		}
 
-		page = compound_head(page);
-
 		/*
 		 * Record which node the original page is from and save this
 		 * information to cc->node_load[].
 		 * Khugepaged will allocate hugepage from the node has the max
 		 * hit record.
 		 */
-		node = page_to_nid(page);
+		node = folio_nid(folio);
 		if (hpage_collapse_scan_abort(node, cc)) {
 			result = SCAN_SCAN_ABORT;
 			goto out_unmap;
 		}
 		cc->node_load[node]++;
-		if (!PageLRU(page)) {
+		if (!folio_test_lru(folio)) {
 			result = SCAN_PAGE_LRU;
 			goto out_unmap;
 		}
-		if (PageLocked(page)) {
+		if (folio_test_locked(folio)) {
 			result = SCAN_PAGE_LOCK;
 			goto out_unmap;
 		}
-		if (!PageAnon(page)) {
+		if (!folio_test_anon(folio)) {
 			result = SCAN_PAGE_ANON;
 			goto out_unmap;
 		}
@@ -1369,7 +1367,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
 		 * has excessive GUP pins (i.e. 512).  Anyway the same check
 		 * will be done again later the risk seems low.
 		 */
-		if (!is_refcount_suitable(page)) {
+		if (!is_refcount_suitable(&folio->page)) {
 			result = SCAN_PAGE_COUNT;
 			goto out_unmap;
 		}
@@ -1379,8 +1377,8 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
 		 * enough young pte to justify collapsing the page
 		 */
 		if (cc->is_khugepaged &&
-		    (pte_young(pteval) || page_is_young(page) ||
-		     PageReferenced(page) || mmu_notifier_test_young(vma->vm_mm,
+		    (pte_young(pteval) || folio_test_young(folio) ||
+		     folio_test_referenced(folio) || mmu_notifier_test_young(vma->vm_mm,
 								     address)))
 			referenced++;
 	}
@@ -1402,7 +1400,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
 		*mmap_locked = false;
 	}
 out:
-	trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
+	trace_mm_khugepaged_scan_pmd(mm, &folio->page, writable, referenced,
 				     none_or_zero, result, unmapped);
 	return result;
 }
-- 
2.40.1