Re: [PATCH] mm: get rid of unnecessary pageblock scanning in setup_zone_migrate_reserve

[KOSAKI Motohiro <kosaki.motohiro@gmail.com>]

> @@ -3926,11 +3929,11 @@ static void setup_zone_migrate_reserve(struct zone *zone)
>   	/*
>   	 * Reserve blocks are generally in place to help high-order atomic
>   	 * allocations that are short-lived. A min_free_kbytes value that
> -	 * would result in more than 2 reserve blocks for atomic allocations
> -	 * is assumed to be in place to help anti-fragmentation for the
> -	 * future allocation of hugepages at runtime.
> +	 * would result in more than MAX_MIGRATE_RESERVE_BLOCKS reserve blocks
> +	 * for atomic allocations is assumed to be in place to help
> +	 * anti-fragmentation for the future allocation of hugepages at runtime.
>   	 */
> -	reserve = min(2, reserve);
> +	reserve = min(MAX_MIGRATE_RESERVE_BLOCKS, reserve);
>
>   	for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
>   		if (!pfn_valid(pfn))
> @@ -3956,6 +3959,7 @@ static void setup_zone_migrate_reserve(struct zone *zone)
>   			/* If this block is reserved, account for it */
>   			if (block_migratetype == MIGRATE_RESERVE) {
>   				reserve--;
> +				found++;
>   				continue;
>   			}
>
> @@ -3970,6 +3974,10 @@ static void setup_zone_migrate_reserve(struct zone *zone)
>   			}
>   		}
>
> +		/* If all possible reserve blocks have been found, we're done */
> +		if (found >= MAX_MIGRATE_RESERVE_BLOCKS)
> +			break;
> +
>   		/*
>   		 * If the reserve is met and this is a previous reserved block,
>   		 * take it back

Nit. I would like to add following hunk. This is just nit because moving
reserve pageblock is extreme rare.

		if (block_migratetype == MIGRATE_RESERVE) {
+                       found++;
			set_pageblock_migratetype(page, MIGRATE_MOVABLE);
			move_freepages_block(zone, page, MIGRATE_MOVABLE);
		}



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