[048/118] mm/page_vma_mapped.c: explicitly compare pfn for normal, hugetlbfs and THP page

Commit Message

Andrew Morton Jan. 31, 2020, 6:13 a.m. UTC

From: Li Xinhai <[e-mail]>
Subject: mm/page_vma_mapped.c: explicitly compare pfn for normal, hugetlbfs and THP page

When check_pte, pfn of normal, hugetlbfs and THP page need be compared. 
The current implementation apply comparison as

- normal 4K page: page_pfn <= pfn < page_pfn + 1
- hugetlbfs page:  page_pfn <= pfn < page_pfn + HPAGE_PMD_NR
- THP page: page_pfn <= pfn < page_pfn + HPAGE_PMD_NR

in pfn_in_hpage.  For hugetlbfs page, it should be page_pfn == pfn

Now, change pfn_in_hpage to pfn_is_match to highlight that comparison is
not only for THP and explicitly compare for these cases.

No impact upon current behavior, just make the code clear.  I think it
is important to make the code clear - comparing hugetlbfs page in range
page_pfn <= pfn < page_pfn + HPAGE_PMD_NR is confusing.

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Li Xinhai <[e-mail]>
Acked-by: Kirill A. Shutemov <[e-mail]>
Acked-by: Mike Kravetz <[e-mail]>
Cc: Kirill A. Shutemov <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/page_vma_mapped.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

Patch

--- a/mm/page_vma_mapped.c~mm-page_vma_mappedc-explicitly-compare-pfn-for-normal-hugetlbfs-and-thp-page
+++ a/mm/page_vma_mapped.c
@@ -52,12 +52,16 @@  static bool map_pte(struct page_vma_mapp
 	return true;
 }
 
-static inline bool pfn_in_hpage(struct page *hpage, unsigned long pfn)
+static inline bool pfn_is_match(struct page *page, unsigned long pfn)
 {
-	unsigned long hpage_pfn = page_to_pfn(hpage);
+	unsigned long page_pfn = page_to_pfn(page);
+
+	/* normal page and hugetlbfs page */
+	if (!PageTransCompound(page) || PageHuge(page))
+		return page_pfn == pfn;
 
 	/* THP can be referenced by any subpage */
-	return pfn >= hpage_pfn && pfn - hpage_pfn < hpage_nr_pages(hpage);
+	return pfn >= page_pfn && pfn - page_pfn < hpage_nr_pages(page);
 }
 
 /**
@@ -108,7 +112,7 @@  static bool check_pte(struct page_vma_ma
 		pfn = pte_pfn(*pvmw->pte);
 	}
 
-	return pfn_in_hpage(pvmw->page, pfn);
+	return pfn_is_match(pvmw->page, pfn);
 }
 
 /**