Re: [RFC 2/8] compaction: make isolate_lru_page with filter aware

[Johannes Weiner]

On Wed, Apr 27, 2011 at 01:25:19AM +0900, Minchan Kim wrote:
> In async mode, compaction doesn't migrate dirty or writeback pages.
> So, it's meaningless to pick the page and re-add it to lru list.
> 
> Of course, when we isolate the page in compaction, the page might
> be dirty or writeback but when we try to migrate the page, the page
> would be not dirty, writeback. So it could be migrated. But it's
> very unlikely as isolate and migration cycle is much faster than
> writeout.
> 
> So, this patch helps cpu and prevent unnecessary LRU churning.
> 
> Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Signed-off-by: Minchan Kim <minchan.kim@xxxxxxxxx>
> ---
>  mm/compaction.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index dea32e3..9f80b5a 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -335,7 +335,7 @@ static unsigned long isolate_migratepages(struct zone *zone,
>  		}
>  
>  		/* Try isolate the page */
> -		if (__isolate_lru_page(page, ISOLATE_BOTH, 0, 0, 0) != 0)
> +		if (__isolate_lru_page(page, ISOLATE_BOTH, 0, !cc->sync, 0) != 0)
>  			continue;

With the suggested flags argument from 1/8, this would look like:

	flags = ISOLATE_BOTH;
	if (!cc->sync)
		flags |= ISOLATE_CLEAN;

?

Anyway, nice change indeed!

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
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