linux-kernel - Re: [PATCH 3/5] mm: compaction: Capture a suitable high-order page immediately when it is made available

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Message-ID: <20120809084110.GA21033@bbox>
Date:	Thu, 9 Aug 2012 17:41:10 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>, Rik van Riel <riel@...hat.com>,
	Jim Schutt <jaschut@...dia.gov>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/5] mm: compaction: Capture a suitable high-order page
 immediately when it is made available

On Thu, Aug 09, 2012 at 09:11:20AM +0100, Mel Gorman wrote:
> On Thu, Aug 09, 2012 at 10:33:58AM +0900, Minchan Kim wrote:
> > Hi Mel,
> > 
> > Just one questoin below.
> > 
> 
> Sure! Your questions usually get me thinking about the right part of the
> series, this series in particular :)
> 
> > > <SNIP>
> > > @@ -708,6 +750,10 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
> > >  				goto out;
> > >  			}
> > >  		}
> > > +
> > > +		/* Capture a page now if it is a suitable size */
> > 
> > Why do we capture only when we migrate MIGRATE_MOVABLE type?
> > If you have a reasone, it should have been added as comment.
> > 
> 
> Good question and there is an answer. However, I also spotted a problem when
> thinking about this more where !MIGRATE_MOVABLE allocations are forced to
> do a full compaction. The simple solution would be to only set cc->page for
> MIGRATE_MOVABLE but there is a better approach that I've implemented in the
> patch below. It includes a comment that should answer your question. Does
> this make sense to you?

It does make sense.
I will add my Reviewed-by in your next spin which includes below patch.

Thanks, Mel.

> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 63af8d2..384164e 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -53,13 +53,31 @@ static inline bool migrate_async_suitable(int migratetype)
>  static void compact_capture_page(struct compact_control *cc)
>  {
>  	unsigned long flags;
> -	int mtype;
> +	int mtype, mtype_low, mtype_high;
>  
>  	if (!cc->page || *cc->page)
>  		return;
>  
> +	/*
> +	 * For MIGRATE_MOVABLE allocations we capture a suitable page ASAP
> +	 * regardless of the migratetype of the freelist is is captured from.
                                                         ^  ^
                                                         typo?
-- 
Kind regards,
Minchan Kim
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