Re: [patch 1/2 v2]compaction: abort compaction loop if lock is contended or run too long

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 10 Sep 2012 09:18:30 +0800
Shaohua Li <shli@kernel.org> wrote:

> isolate_migratepages_range() might isolate none pages, for example, when
> zone->lru_lock is contended and compaction is async. In this case, we should
> abort compaction, otherwise, compact_zone will run a useless loop and make
> zone->lru_lock is even contended.
> 
> ...
>
> @@ -838,12 +838,14 @@ static unsigned long compact_zone_order(
>  		.migratetype = allocflags_to_migratetype(gfp_mask),
>  		.zone = zone,
>  		.sync = sync,
> -		.contended = contended,
>  	};
>  	INIT_LIST_HEAD(&cc.freepages);
>  	INIT_LIST_HEAD(&cc.migratepages);
>  
> -	return compact_zone(zone, &cc);
> +	ret = compact_zone(zone, &cc);
> +	if (contended)
> +		*contended = cc.contended;
> +	return ret;
>  }
>  

>From a quick read, `contended' is never NULL here.  And defining the
interface so that `contended' must be a valid pointer is a good change,
IMO - it results in simpler and faster code.

Alas, try_to_compact_pages()'s kerneldoc altogether forgets to describe
this argument.  Mel's
mm-compaction-capture-a-suitable-high-order-page-immediately-when-it-is-made-available.patch
adds a `pages' arg and forgets to document that as well.

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>