Re: [PATCH] Properly account for freed pages in free_pages_bulk()and when allocating high-order pages in buffered_rmqueue() V2

[Hugh Dickins]

On Tue, 28 Apr 2009, Mel Gorman wrote:

> free_pages_bulk() updates the number of free pages in the zone but it is
> assuming that the pages being freed are order-0. While this is currently
> always true, it's wrong to assume the order is 0. This patch fixes the problem.
> 
> buffered_rmqueue() is not updating NR_FREE_PAGES when allocating pages with
> __rmqueue(). As a result, high-order allocation will appear to increase
> the number of free pages leading to the situation where the free page count
> exceeds available RAM. This patch accounts for those allocated pages properly.
> 
> This is a fix for page-allocator-update-nr_free_pages-only-as-necessary.patch.
> 
> Changelog since V1
>   o Change 1UL to 1 as it's unnecessary in this case to be unsigned long
> 
> Reported-by: Zhang, Yanmin <yanmin_zhang@xxxxxxxxxxxxxxx>
> Signed-off-by: Mel Gorman <mel@xxxxxxxxx>

Thanks, Mel!  (And I don't need to test it, since it's now
remarkably similar to a patch I was preparing yesterday.)

Acked-by: Hugh Dickins <hugh@xxxxxxxxxxx>

> --- 
>  mm/page_alloc.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5dd2d59..59eb2e1 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -545,7 +545,7 @@ static void free_pages_bulk(struct zone *zone, int count,
>  	zone_clear_flag(zone, ZONE_ALL_UNRECLAIMABLE);
>  	zone->pages_scanned = 0;
>  
> -	__mod_zone_page_state(zone, NR_FREE_PAGES, count);
> +	__mod_zone_page_state(zone, NR_FREE_PAGES, count << order);
>  	while (count--) {
>  		struct page *page;
>  
> @@ -1151,6 +1151,7 @@ again:
>  	} else {
>  		spin_lock_irqsave(&zone->lock, flags);
>  		page = __rmqueue(zone, order, migratetype);
> +		__mod_zone_page_state(zone, NR_FREE_PAGES, -(1 << order));
>  		spin_unlock(&zone->lock);
>  		if (!page)
>  			goto failed;
--
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