Re: [PATCH] mm: compaction: Abort compaction if too many pages areisolated and caller is asynchronous

[Minchan Kim]

On Mon, May 30, 2011 at 02:13:00PM +0100, Mel Gorman wrote:
> Asynchronous compaction is used when promoting to huge pages. This is
> all very nice but if there are a number of processes in compacting
> memory, a large number of pages can be isolated. An "asynchronous"
> process can stall for long periods of time as a result with a user
> reporting that firefox can stall for 10s of seconds. This patch aborts
> asynchronous compaction if too many pages are isolated as it's better to
> fail a hugepage promotion than stall a process.
> 
> If accepted, this should also be considered for 2.6.39-stable. It should
> also be considered for 2.6.38-stable but ideally [11bc82d6: mm:
> compaction: Use async migration for __GFP_NO_KSWAPD and enforce no
> writeback] would be applied to 2.6.38 before consideration.
> 
> Reported-and-Tested-by: Ury Stankevich <urykhy@xxxxxxxxx>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx>

I have a nitpick below.
Otherwise, looks good to me.

> ---
>  mm/compaction.c |   32 ++++++++++++++++++++++++++------
>  1 files changed, 26 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 021a296..331a2ee 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -240,11 +240,20 @@ static bool too_many_isolated(struct zone *zone)
>  	return isolated > (inactive + active) / 2;
>  }
>  
> +/* possible outcome of isolate_migratepages */
> +typedef enum {
> +	ISOLATE_ABORT,		/* Abort compaction now */
> +	ISOLATE_NONE,		/* No pages isolated, continue scanning */
> +	ISOLATE_SUCCESS,	/* Pages isolated, migrate */
> +} isolate_migrate_t;
> +
>  /*
>   * Isolate all pages that can be migrated from the block pointed to by
>   * the migrate scanner within compact_control.
> + *
> + * Returns false if compaction should abort at this point due to congestion.

false? I think it would be better to use explicit word, ISOLATE_ABORT.

-- 
Kind regards
Minchan Kim
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