[v19,05/20] mm/thp: Simplify lru_add_page_tail()

Commit Message

Alex Shi Sept. 24, 2020, 3:28 a.m. UTC

Simplify lru_add_page_tail(), there are actually only two cases possible:
split_huge_page_to_list(), with list supplied and head isolated from lru
by its caller; or split_huge_page(), with NULL list and head on lru -
because when head is racily isolated from lru, the isolator's reference
will stop the split from getting any further than its page_ref_freeze().

So decide between the two cases by "list", but add VM_WARN_ON()s to
verify that they match our lru expectations.

[Hugh Dickins: rewrite commit log]
Signed-off-by: Alex Shi <[e-mail]>
Reviewed-by: Kirill A. Shutemov <[e-mail]>
Acked-by: Hugh Dickins <[e-mail]>
Cc: Kirill A. Shutemov <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Johannes Weiner <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Mika Penttilä <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
---
 mm/huge_memory.c | 21 ++++++---------------
 1 file changed, 6 insertions(+), 15 deletions(-)

Patch

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index fa0753229b52..8b92cd197218 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2326,25 +2326,16 @@  static void lru_add_page_tail(struct page *head, struct page *page_tail,
 	VM_BUG_ON_PAGE(PageLRU(page_tail), head);
 	lockdep_assert_held(&lruvec_pgdat(lruvec)->lru_lock);
 
-	if (!list)
-		SetPageLRU(page_tail);
-
-	if (likely(PageLRU(head)))
-		list_add_tail(&page_tail->lru, &head->lru);
-	else if (list) {
+	if (list) {
 		/* page reclaim is reclaiming a huge page */
+		VM_WARN_ON(PageLRU(head));
 		get_page(page_tail);
 		list_add_tail(&page_tail->lru, list);
 	} else {
-		/*
-		 * Head page has not yet been counted, as an hpage,
-		 * so we must account for each subpage individually.
-		 *
-		 * Put page_tail on the list at the correct position
-		 * so they all end up in order.
-		 */
-		add_page_to_lru_list_tail(page_tail, lruvec,
-					  page_lru(page_tail));
+		/* head is still on lru (and we have it frozen) */
+		VM_WARN_ON(!PageLRU(head));
+		SetPageLRU(page_tail);
+		list_add_tail(&page_tail->lru, &head->lru);
 	}
 }