Re: [PATCH v2 2/5] mm/compaction: do not call suitable_migration_target() on every page

[Vlastimil Babka]

On 02/14/2014 07:54 AM, Joonsoo Kim wrote:
> suitable_migration_target() checks that pageblock is suitable for
> migration target. In isolate_freepages_block(), it is called on every
> page and this is inefficient. So make it called once per pageblock.
>
> suitable_migration_target() also checks if page is highorder or not,
> but it's criteria for highorder is pageblock order. So calling it once
> within pageblock range has no problem.
>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>

> diff --git a/mm/compaction.c b/mm/compaction.c
> index bbe1260..0d821a2 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -245,6 +245,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
>   	unsigned long nr_strict_required = end_pfn - blockpfn;
>   	unsigned long flags;
>   	bool locked = false;
> +	bool checked_pageblock = false;
>
>   	cursor = pfn_to_page(blockpfn);
>
> @@ -275,8 +276,16 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
>   			break;
>
>   		/* Recheck this is a suitable migration target under lock */
> -		if (!strict && !suitable_migration_target(page))
> -			break;
> +		if (!strict && !checked_pageblock) {
> +			/*
> +			 * We need to check suitability of pageblock only once
> +			 * and this isolate_freepages_block() is called with
> +			 * pageblock range, so just check once is sufficient.
> +			 */
> +			checked_pageblock = true;
> +			if (!suitable_migration_target(page))
> +				break;
> +		}
>
>   		/* Recheck this is a buddy page under lock */
>   		if (!PageBuddy(page))

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