[RFC]handle error of rmqueue_bulk

[RFC]handle error of rmqueue_bulk

[Shaohua Li]

if rmqueue_bulk fails, we might get page with wrong migratetype,
shouldn't we consider the case? 

Thanks,
Shaohua

Index: linux/mm/page_alloc.c
===================================================================
--- linux.orig/mm/page_alloc.c	2007-12-14 16:44:35.000000000 +0800
+++ linux/mm/page_alloc.c	2007-12-14 16:45:42.000000000 +0800
@@ -1067,8 +1067,12 @@ again:
 
 		/* Allocate more to the pcp list if necessary */
 		if (unlikely(&page->lru == &pcp->list)) {
-			pcp->count += rmqueue_bulk(zone, 0,
+			int cn;
+			cn = rmqueue_bulk(zone, 0,
 					pcp->batch, &pcp->list, migratetype);
+			if (unlikely(!cn))
+				goto failed;
+			pcp->count += cn;
 			page = list_entry(pcp->list.next, struct page, lru);
 		}
 

Re: [RFC]handle error of rmqueue_bulk

[Mel Gorman]

On (14/12/07 17:08), Shaohua Li didst pronounce:
> if rmqueue_bulk fails, we might get page with wrong migratetype,
> shouldn't we consider the case? 
> 

No. It is not a page allocation failure when this occurs, at worst
fragmentation gets a little worse. At this point, it is known the
per-cpu list contains pages so if one of the appropriate migrate type
cannot be found, fragmentation is allowed to get a little worse instead
of failing.

> Thanks,
> Shaohua
> 
> Index: linux/mm/page_alloc.c
> ===================================================================
> --- linux.orig/mm/page_alloc.c	2007-12-14 16:44:35.000000000 +0800
> +++ linux/mm/page_alloc.c	2007-12-14 16:45:42.000000000 +0800
> @@ -1067,8 +1067,12 @@ again:
>  
>  		/* Allocate more to the pcp list if necessary */
>  		if (unlikely(&page->lru == &pcp->list)) {
> -			pcp->count += rmqueue_bulk(zone, 0,
> +			int cn;
> +			cn = rmqueue_bulk(zone, 0,
>  					pcp->batch, &pcp->list, migratetype);
> +			if (unlikely(!cn))
> +				goto failed;
> +			pcp->count += cn;
>  			page = list_entry(pcp->list.next, struct page, lru);
>  		}
>  
> 
> 

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab