[PATCH v2 1/2] mm: fix contiguous memmap assumptions about split page

[Chen Wandun <chenwandun@huawei.com>]

It isn't true for only SPARSEMEM configs to assume that a compound page
has virtually contiguous page structs, so use nth_page to iterate each
page.

Inspired by:
https://lore.kernel.org/linux-mm/20220204195852.1751729-8-willy@infradead.org/

Signed-off-by: Chen Wandun <chenwandun@huawei.com>
---
 mm/compaction.c  | 6 +++---
 mm/huge_memory.c | 2 +-
 mm/page_alloc.c  | 2 +-
 3 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index c3e37aa9ff9e..ddff13b968a2 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -87,7 +87,7 @@ static unsigned long release_freepages(struct list_head *freelist)
 static void split_map_pages(struct list_head *list)
 {
 	unsigned int i, order, nr_pages;
-	struct page *page, *next;
+	struct page *page, *next, *tmp;
 	LIST_HEAD(tmp_list);
 
 	list_for_each_entry_safe(page, next, list, lru) {
@@ -101,8 +101,8 @@ static void split_map_pages(struct list_head *list)
 			split_page(page, order);
 
 		for (i = 0; i < nr_pages; i++) {
-			list_add(&page->lru, &tmp_list);
-			page++;
+			tmp = nth_page(page, i);
+			list_add(&tmp->lru, &tmp_list);
 		}
 	}
 
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 2fe38212e07c..d77fc2ad581d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2297,7 +2297,7 @@ static void lru_add_page_tail(struct page *head, struct page *tail,
 static void __split_huge_page_tail(struct page *head, int tail,
 		struct lruvec *lruvec, struct list_head *list)
 {
-	struct page *page_tail = head + tail;
+	struct page *page_tail = nth_page(head, tail);
 
 	VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
 
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f648decfe39d..855211dea13e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3513,7 +3513,7 @@ void split_page(struct page *page, unsigned int order)
 	VM_BUG_ON_PAGE(!page_count(page), page);
 
 	for (i = 1; i < (1 << order); i++)
-		set_page_refcounted(page + i);
+		set_page_refcounted(nth_page(page, i));
 	split_page_owner(page, 1 << order);
 	split_page_memcg(page, 1 << order);
 }
-- 
2.18.0.huawei.25