Re: [PATCH 2/3] page-allocator: Check zone pressure when batch ofpages are freed

[Nick Piggin]

Cool, you found this doesn't hurt performance too much?

Can't you remove the check from the reclaim code now? (The check
here should give a more timely wait anyway)

This is good because it should eliminate most all cases of extra
waiting. I wonder if you've also thought of doing the check in the
allocation path too as we were discussing? (this would give a better
FIFO behaviour under memory pressure but I could easily agree it is not
worth the cost)

On Mon, Mar 08, 2010 at 11:48:22AM +0000, Mel Gorman wrote:
> When a batch of pages have been freed to the buddy allocator, it is possible
> that it is enough to push a zone above its watermarks. This patch puts a
> check in the free path for zone pressure. It's in a common path but for
> the most part, it should only be checking if a linked list is empty and
> have minimal performance impact.
> 
> Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
> ---
>  mm/page_alloc.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 1383ff9..3c8e8b7 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -562,6 +562,9 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>  		} while (--count && --batch_free && !list_empty(list));
>  	}
>  	spin_unlock(&zone->lock);
> +
> +	/* A batch of pages have been freed so check zone pressure */
> +	check_zone_pressure(zone);
>  }
>  
>  static void free_one_page(struct zone *zone, struct page *page, int order,
> -- 
> 1.6.5
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