Re: [patch v2 4/4]thp: improve order in lru list for split huge page

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

On Wed, 2011-11-23 at 07:40 +0800, Andrew Morton wrote:
> On Tue, 15 Nov 2011 15:04:21 +0800
> Shaohua Li <shaohua.li@intel.com> wrote:
> 
> > Put the tail subpages of an isolated hugepage under splitting in the
> > lru reclaim head as they supposedly should be isolated too next.
> > 
> > Queues the subpages in physical order in the lru for non isolated
> > hugepages under splitting. That might provide some theoretical cache
> > benefit to the buddy allocator later.
> > 
> > ...
> >
> > --- linux.orig/mm/swap.c	2011-11-14 16:12:03.000000000 +0800
> > +++ linux/mm/swap.c	2011-11-15 09:15:33.000000000 +0800
> > @@ -684,7 +684,7 @@ 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);
> 
> This conflicts with changes in Johannes's "mm: collect LRU list heads
> into struct lruvec":
> 
> @@ -674,10 +673,10 @@ void lru_add_page_tail(struct zone* zone
>  		}
>  		update_page_reclaim_stat(zone, page_tail, file, active);
>  		if (likely(PageLRU(page)))
> -			head = page->lru.prev;
> +			__add_page_to_lru_list(zone, page_tail, lru,
> +					       page->lru.prev);
>  		else
> -			head = &zone->lru[lru].list;
> -		__add_page_to_lru_list(zone, page_tail, lru, head);
> +			add_page_to_lru_list(zone, page_tail, lru);
>  	} else {
>  		SetPageUnevictable(page_tail);
>  		add_page_to_lru_list(zone, page_tail, LRU_UNEVICTABLE);
Here is the patch applied to linux-next.

Put the tail subpages of an isolated hugepage under splitting in the
lru reclaim head as they supposedly should be isolated too next.

Queues the subpages in physical order in the lru for non isolated
hugepages under splitting. That might provide some theoretical cache
benefit to the buddy allocator later.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
---
 mm/huge_memory.c |    5 ++---
 mm/swap.c        |    2 +-
 2 files changed, 3 insertions(+), 4 deletions(-)

Index: linux/mm/huge_memory.c
===================================================================
--- linux.orig/mm/huge_memory.c	2011-11-23 10:47:16.000000000 +0800
+++ linux/mm/huge_memory.c	2011-11-23 11:22:55.000000000 +0800
@@ -1228,7 +1228,6 @@ 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;
 	int tail_count = 0;
@@ -1237,7 +1236,7 @@ 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->_mapcount cannot change */
@@ -1300,7 +1299,7 @@ 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	2011-11-23 10:58:05.000000000 +0800
+++ linux/mm/swap.c	2011-11-23 11:06:38.000000000 +0800
@@ -681,7 +681,7 @@ void lru_add_page_tail(struct zone* zone
 		if (likely(PageLRU(page)))
 			list_add(&page_tail->lru, page->lru.prev);
 		else
-			list_add(&page_tail->lru, &lruvec->lists[lru]);
+			list_add(&page_tail->lru, lruvec->lists[lru].prev);
 		__mod_zone_page_state(zone, NR_LRU_BASE + lru,
 				      hpage_nr_pages(page_tail));
 	} else {


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