mm/ksm: convert get_mergeable_page() from follow_page() to folio_walk

Let's use folio_walk instead, for example avoiding taking temporary folio
references if the folio does not even apply and getting rid of one more
follow_page() user.

Note that zeropages obviously don't apply: old code could just have
specified FOLL_DUMP.  Anon folios are never secretmem, so we don't care
about losing the check in follow_page().

Link: https://lkml.kernel.org/r/20240802155524.517137-6-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 14 insertions, 12 deletions

diff --git a/mm/ksm.c b/mm/ksm.c
index 14d9e53b1ec2..742b005f3f77 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -767,26 +767,28 @@ static struct page *get_mergeable_page(struct ksm_rmap_item *rmap_item)
 	struct mm_struct *mm = rmap_item->mm;
 	unsigned long addr = rmap_item->address;
 	struct vm_area_struct *vma;
-	struct page *page;
+	struct page *page = NULL;
+	struct folio_walk fw;
+	struct folio *folio;
 
 	mmap_read_lock(mm);
 	vma = find_mergeable_vma(mm, addr);
 	if (!vma)
 		goto out;
 
-	page = follow_page(vma, addr, FOLL_GET);
-	if (IS_ERR_OR_NULL(page))
-		goto out;
-	if (is_zone_device_page(page))
-		goto out_putpage;
-	if (PageAnon(page)) {
+	folio = folio_walk_start(&fw, vma, addr, 0);
+	if (folio) {
+		if (!folio_is_zone_device(folio) &&
+		    folio_test_anon(folio)) {
+			folio_get(folio);
+			page = fw.page;
+		}
+		folio_walk_end(&fw, vma);
+	}
+out:
+	if (page) {
 		flush_anon_page(vma, page, addr);
 		flush_dcache_page(page);
-	} else {
-out_putpage:
-		put_page(page);
-out:
-		page = NULL;
 	}
 	mmap_read_unlock(mm);
 	return page;