Re: CMA broken in next-20120926

[Mel Gorman]

On Tue, Oct 09, 2012 at 10:40:10AM +0200, Bartlomiej Zolnierkiewicz wrote:
> I also need following patch to make CONFIG_CMA=y && CONFIG_COMPACTION=y case
> work:
> 
> From: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
> Subject: [PATCH] mm: compaction: cache if a pageblock was scanned and no pages were isolated - cma fix
> 
> Patch "mm: compaction: cache if a pageblock was scanned and no pages
> were isolated" needs a following fix to successfully boot next-20121002
> kernel (same with next-20121008) with CONFIG_CMA=y and CONFIG_COMPACTION=y
> (with applied -fix1, -fix2, -fix3 patches from Mel Gorman and also with
> cmatest module from Thierry Reding compiled in).
> 

Why is it needed to make it boot? CMA should not care about the
PG_migrate_skip hint being set because it should always ignore it in
alloc_contig_range() due to cc->ignore_skip_hint. It's not obvious to
me why this fixes a boot failure and I wonder if it's papering over some
underlying problem. Can you provide more details please?

> Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx>
> Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
> ---
>  mm/compaction.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> Index: b/mm/compaction.c
> ===================================================================
> --- a/mm/compaction.c	2012-10-08 18:10:53.491679716 +0200
> +++ b/mm/compaction.c	2012-10-08 18:11:33.615679713 +0200
> @@ -117,7 +117,8 @@ static void update_pageblock_skip(struct
>  			bool migrate_scanner)
>  {
>  	struct zone *zone = cc->zone;
> -	if (!page)
> +
> +	if (!page || cc->ignore_skip_hint)
>  		return;
>  
>  	if (!nr_isolated) {

-- 
Mel Gorman
SUSE Labs
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