[PATCH v2 1/2] mm: khugepaged: convert set_huge_pmd() to take a folio

[Baolin Wang]

We've already gotten the stable locked folio in collapse_pte_mapped_thp(),
so just use folio for set_huge_pmd() to set the PMD entry, which is more
straightforward.

Moreover, we will check the folio size in do_set_pmd(), so we can remove
the unnecessary VM_BUG_ON() in set_huge_pmd(). While we are at it, we can
also remove the PageTransHuge(), as it currently has no callers.

Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
Changes from v1:
 - Remove the unnecessary VM_BUG_ON().
 - Remove the PageTransHuge().
---
 include/linux/page-flags.h | 15 ---------------
 mm/khugepaged.c            |  9 ++++-----
 2 files changed, 4 insertions(+), 20 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 37b11f15dbd9..1c1d49554c71 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -907,20 +907,6 @@ FOLIO_FLAG_FALSE(partially_mapped)
 #define PG_head_mask ((1UL << PG_head))
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-/*
- * PageHuge() only returns true for hugetlbfs pages, but not for
- * normal or transparent huge pages.
- *
- * PageTransHuge() returns true for both transparent huge and
- * hugetlbfs pages, but not normal pages. PageTransHuge() can only be
- * called only in the core VM paths where hugetlbfs pages can't exist.
- */
-static inline int PageTransHuge(const struct page *page)
-{
-	VM_BUG_ON_PAGE(PageTail(page), page);
-	return PageHead(page);
-}
-
 /*
  * PageTransCompound returns true for both transparent huge pages
  * and hugetlbfs pages, so it should only be called when it's known
@@ -931,7 +917,6 @@ static inline int PageTransCompound(const struct page *page)
 	return PageCompound(page);
 }
 #else
-TESTPAGEFLAG_FALSE(TransHuge, transhuge)
 TESTPAGEFLAG_FALSE(TransCompound, transcompound)
 #endif
 
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index b04b6a770afe..aca66e7f4fd9 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1467,7 +1467,7 @@ static void collect_mm_slot(struct khugepaged_mm_slot *mm_slot)
 #ifdef CONFIG_SHMEM
 /* hpage must be locked, and mmap_lock must be held */
 static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
-			pmd_t *pmdp, struct page *hpage)
+			pmd_t *pmdp, struct folio *folio)
 {
 	struct vm_fault vmf = {
 		.vma = vma,
@@ -1476,13 +1476,12 @@ static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
 		.pmd = pmdp,
 	};
 
-	VM_BUG_ON(!PageTransHuge(hpage));
 	mmap_assert_locked(vma->vm_mm);
 
-	if (do_set_pmd(&vmf, hpage))
+	if (do_set_pmd(&vmf, &folio->page))
 		return SCAN_FAIL;
 
-	get_page(hpage);
+	folio_get(folio);
 	return SCAN_SUCCEED;
 }
 
@@ -1689,7 +1688,7 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
 maybe_install_pmd:
 	/* step 5: install pmd entry */
 	result = install_pmd
-			? set_huge_pmd(vma, haddr, pmd, &folio->page)
+			? set_huge_pmd(vma, haddr, pmd, folio)
 			: SCAN_SUCCEED;
 	goto drop_folio;
 abort:
-- 
2.43.5