[patch 03/19] mm/thp: simplify lru_add_page_tail()

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From: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Subject: mm/thp: simplify lru_add_page_tail()

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]
Link: https://lkml.kernel.org/r/1604566549-62481-4-git-send-email-alex.shi@xxxxxxxxxxxxxxxxx
Signed-off-by: Alex Shi <alex.shi@xxxxxxxxxxxxxxxxx>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Acked-by: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Mika Penttilä <mika.penttila@xxxxxxxxxxxx>
Cc: Alexander Duyck <alexander.duyck@xxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: "Chen, Rong A" <rong.a.chen@xxxxxxxxx>
Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Jann Horn <jannh@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Shakeel Butt <shakeelb@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vladimir Davydov <vdavydov.dev@xxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Wei Yang <richard.weiyang@xxxxxxxxx>
Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/huge_memory.c |   20 ++++++--------------
 1 file changed, 6 insertions(+), 14 deletions(-)

--- a/mm/huge_memory.c~mm-thp-simplify-lru_add_page_tail
+++ a/mm/huge_memory.c
@@ -2367,24 +2367,16 @@ static void lru_add_page_tail(struct pag
 	VM_BUG_ON_PAGE(PageLRU(tail), head);
 	lockdep_assert_held(&lruvec_pgdat(lruvec)->lru_lock);
 
-	if (!list)
-		SetPageLRU(tail);
-
-	if (likely(PageLRU(head)))
-		list_add_tail(&tail->lru, &head->lru);
-	else if (list) {
+	if (list) {
 		/* page reclaim is reclaiming a huge page */
+		VM_WARN_ON(PageLRU(head));
 		get_page(tail);
 		list_add_tail(&tail->lru, list);
 	} else {
-		/*
-		 * Head page has not yet been counted, as an hpage,
-		 * so we must account for each subpage individually.
-		 *
-		 * Put tail on the list at the correct position
-		 * so they all end up in order.
-		 */
-		add_page_to_lru_list_tail(tail, lruvec, page_lru(tail));
+		/* head is still on lru (and we have it frozen) */
+		VM_WARN_ON(!PageLRU(head));
+		SetPageLRU(tail);
+		list_add_tail(&tail->lru, &head->lru);
 	}
 }
 
_




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