Commit 8df651c7 authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds

thp: cleanup split_huge_page()

After one of bugfixes to freeze_page(), we don't have freezed pages in
rmap, therefore mapcount of all subpages of freezed THP is zero.  And we
have assert for that.

Let's drop code which deal with non-zero mapcount of subpages.
Signed-off-by: default avatarKirill A. Shutemov <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 88193f7c
......@@ -3220,28 +3220,26 @@ static void unfreeze_page(struct anon_vma *anon_vma, struct page *page)
static int __split_huge_page_tail(struct page *head, int tail,
static void __split_huge_page_tail(struct page *head, int tail,
struct lruvec *lruvec, struct list_head *list)
int mapcount;
struct page *page_tail = head + tail;
mapcount = atomic_read(&page_tail->_mapcount) + 1;
VM_BUG_ON_PAGE(atomic_read(&page_tail->_mapcount) != -1, page_tail);
VM_BUG_ON_PAGE(atomic_read(&page_tail->_count) != 0, page_tail);
* tail_page->_count is zero and not changing from under us. But
* get_page_unless_zero() may be running from under us on the
* tail_page. If we used atomic_set() below instead of atomic_add(), we
* tail_page. If we used atomic_set() below instead of atomic_inc(), we
* would then run atomic_set() concurrently with
* get_page_unless_zero(), and atomic_set() is implemented in C not
* using locked ops. spin_unlock on x86 sometime uses locked ops
* because of PPro errata 66, 92, so unless somebody can guarantee
* atomic_set() here would be safe on all archs (and not only on x86),
* it's safer to use atomic_add().
* it's safer to use atomic_inc().
atomic_add(mapcount + 1, &page_tail->_count);
page_tail->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
page_tail->flags |= (head->flags &
......@@ -3275,8 +3273,6 @@ static int __split_huge_page_tail(struct page *head, int tail,
page_tail->index = head->index + tail;
page_cpupid_xchg_last(page_tail, page_cpupid_last(head));
lru_add_page_tail(head, page_tail, lruvec, list);
return mapcount;
static void __split_huge_page(struct page *page, struct list_head *list)
......@@ -3284,7 +3280,7 @@ static void __split_huge_page(struct page *page, struct list_head *list)
struct page *head = compound_head(page);
struct zone *zone = page_zone(head);
struct lruvec *lruvec;
int i, tail_mapcount;
int i;
/* prevent PageLRU to go away from under us, and freeze lru stats */
......@@ -3293,10 +3289,8 @@ static void __split_huge_page(struct page *page, struct list_head *list)
/* complete memcg works before add pages to LRU */
tail_mapcount = 0;
for (i = HPAGE_PMD_NR - 1; i >= 1; i--)
tail_mapcount += __split_huge_page_tail(head, i, lruvec, list);
atomic_sub(tail_mapcount, &head->_count);
__split_huge_page_tail(head, i, lruvec, list);
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