[patch 4/5]thp: correct order in lru list for split huge page

[Shaohua Li <shaohua.li@intel.com>]

If a huge page is split, all the subpages should live in lru list adjacently
because they should be taken as a whole.
In page split, with current code:
a. if huge page is in lru list, the order is: page, page+HPAGE_PMD_NR-1,
page + HPAGE_PMD_NR-2, ..., page + 1(in lru page reclaim order)
b. otherwise, the order is: page, ..other pages.., page + 1, page + 2, ...(in
lru page reclaim order). page + 1 ... page + HPAGE_PMD_NR - 1 are in the lru
reclaim tail.

In case a, the order is wrong. In case b, page is isolated (to be reclaimed),
but other tail pages will not soon.

With below patch:
in case a, the order is: page, page + 1, ... page + HPAGE_PMD_NR-1(in lru page
reclaim order).
in case b, the order is: page + 1, ... page + HPAGE_PMD_NR-1 (in lru page reclaim
order). The tail pages are in the lru reclaim head.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
---
 mm/huge_memory.c |    5 ++---
 mm/swap.c        |    5 +++--
 2 files changed, 5 insertions(+), 5 deletions(-)

Index: linux/mm/huge_memory.c
===================================================================
--- linux.orig/mm/huge_memory.c	2011-10-25 09:06:55.000000000 +0800
+++ linux/mm/huge_memory.c	2011-10-25 09:31:07.000000000 +0800
@@ -1162,7 +1162,6 @@ static int __split_huge_page_splitting(s
 static void __split_huge_page_refcount(struct page *page)
 {
 	int i;
-	unsigned long head_index = page->index;
 	struct zone *zone = page_zone(page);
 	int zonestat;
 
@@ -1170,7 +1169,7 @@ static void __split_huge_page_refcount(s
 	spin_lock_irq(&zone->lru_lock);
 	compound_lock(page);
 
-	for (i = 1; i < HPAGE_PMD_NR; i++) {
+	for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
 		struct page *page_tail = page + i;
 
 		/* tail_page->_count cannot change */
@@ -1221,7 +1220,7 @@ static void __split_huge_page_refcount(s
 		BUG_ON(page_tail->mapping);
 		page_tail->mapping = page->mapping;
 
-		page_tail->index = ++head_index;
+		page_tail->index = page->index + i;
 
 		BUG_ON(!PageAnon(page_tail));
 		BUG_ON(!PageUptodate(page_tail));
Index: linux/mm/swap.c
===================================================================
--- linux.orig/mm/swap.c	2011-10-25 08:36:09.000000000 +0800
+++ linux/mm/swap.c	2011-10-25 09:31:07.000000000 +0800
@@ -661,11 +661,12 @@ void lru_add_page_tail(struct zone* zone
 		if (likely(PageLRU(page)))
 			head = page->lru.prev;
 		else
-			head = &zone->lru[lru].list;
+			head = zone->lru[lru].list.prev;
 		__add_page_to_lru_list(zone, page_tail, lru, head);
 	} else {
 		SetPageUnevictable(page_tail);
-		add_page_to_lru_list(zone, page_tail, LRU_UNEVICTABLE);
+		head = zone->lru[LRU_UNEVICTABLE].list.prev;
+		__add_page_to_lru_list(zone, page_tail, LRU_UNEVICTABLE, head);
 	}
 }
 


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