[2/2] mm/memory_hotplug: remove head page reference in scan_movable_pages()

Commit Message

Sidhartha Kumar Jan. 23, 2023, 8:23 p.m. UTC

Remove one user of the Huge Page macros which take in a page. Also remove
a reference to a head page variable by using a folio instead.

Signed-off-by: Sidhartha Kumar <[e-mail]>
---
 mm/memory_hotplug.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

Comments

Matthew Wilcox Jan. 23, 2023, 8:39 p.m. UTC | #1

On Mon, Jan 23, 2023 at 12:23:47PM -0800, Sidhartha Kumar wrote:
> -		if (!PageHuge(page))
> +		folio = page_folio(page);
> +		if (!folio_test_hugetlb(folio))
>  			continue;
> -		head = compound_head(page);
>  		/*
>  		 * This test is racy as we hold no reference or lock.  The
>  		 * hugetlb page could have been free'ed and head is no longer

Assuming the comment is correct, this patch is also unsafe.

Patch

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index ad09189786b1..d5a0672cdf3a 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1579,7 +1579,8 @@  static int scan_movable_pages(unsigned long start, unsigned long end,
 	unsigned long pfn;
 
 	for (pfn = start; pfn < end; pfn++) {
-		struct page *page, *head;
+		struct page *page;
+		struct folio *folio;
 		unsigned long skip;
 
 		if (!pfn_valid(pfn))
@@ -1599,9 +1600,9 @@  static int scan_movable_pages(unsigned long start, unsigned long end,
 		if (PageOffline(page) && page_count(page))
 			return -EBUSY;
 
-		if (!PageHuge(page))
+		folio = page_folio(page);
+		if (!folio_test_hugetlb(folio))
 			continue;
-		head = compound_head(page);
 		/*
 		 * This test is racy as we hold no reference or lock.  The
 		 * hugetlb page could have been free'ed and head is no longer
@@ -1609,9 +1610,9 @@  static int scan_movable_pages(unsigned long start, unsigned long end,
 		 * cases false positives and negatives are possible.  Calling
 		 * code must deal with these scenarios.
 		 */
-		if (HPageMigratable(head))
+		if (folio_test_hugetlb_migratable(folio))
 			goto found;
-		skip = compound_nr(head) - (page - head);
+		skip = folio_nr_pages(folio) - (page - &folio->page);
 		pfn += skip - 1;
 	}
 	return -ENOENT;