Re: [PATCH] mm: Add unlikely for current_order test

From: David Rientjes
Date: Sun Jun 16 2013 - 14:04:57 EST


On Sat, 15 Jun 2013, Zhang Yanfei wrote:

> From: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx>
>
> Since we have an unlikely for the "current_order >= pageblock_order / 2"
> test above, adding an unlikely for this "current_order >= pageblock_order"
> test seems more appropriate.
>

I don't understand the justification at all, current_order being unlikely
greater than or equal to pageblock_order / 2 doesn't imply at all that
it's unlikely that current_order is greater than or equal to
pageblock_order.

> Signed-off-by: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx>
> ---
> mm/page_alloc.c | 2 +-
> 1 files changed, 1 insertions(+), 1 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c3edb62..1b6d7de 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1071,7 +1071,7 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype)
> rmv_page_order(page);
>
> /* Take ownership for orders >= pageblock_order */
> - if (current_order >= pageblock_order &&
> + if (unlikely(current_order >= pageblock_order) &&
> !is_migrate_cma(migratetype))
> change_pageblock_range(page, current_order,
> start_migratetype);
--
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