linux-kernel - Re: kswapd skips compaction if reclaim order drops to zero?

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Message-ID: <20130815134139.GC8437@gmail.com>
Date:	Thu, 15 Aug 2013 22:41:39 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Hillf Danton <dhillf@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-MM <linux-mm@...ck.org>
Subject: Re: kswapd skips compaction if reclaim order drops to zero?

Hey Mel,

On Thu, Aug 15, 2013 at 11:47:27AM +0100, Mel Gorman wrote:
> On Thu, Aug 15, 2013 at 06:02:53PM +0800, Hillf Danton wrote:
> > If the allocation order is not high, direct compaction does nothing.
> > Can we skip compaction here if order drops to zero?
> > 
> 
> If the allocation order is not high then
> 
> pgdat_needs_compaction == (order > 0) == false == no calling compact_pdatt
> 
> In the case where order is reset to 0 due to fragmentation then it does
> call compact_pgdat but it does no work due to the cc->order check in
> __compact_pgdat.
> 

I am looking at mmotm-2013-08-07-16-55 but couldn't find cc->order
check right before compact_zone in __comact_pgdat.
Could you pinpoint code piece?

> -- 
> Mel Gorman
> SUSE Labs
> 
> --
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-- 
Kind regards,
Minchan Kim
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