linux-kernel - Re: [PATCH v2] mm/compaction: __compact

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Date:	Wed, 25 Nov 2015 02:45:15 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Joonsoo Kim <js1304@...il.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Vlastimil Babka <vbabka@...e.cz>, Mel Gorman <mgorman@...e.de>,
	Yaowei Bai <bywxiaobai@....com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v2] mm/compaction: __compact_pgdat() code cleanuup

On Wed, 25 Nov 2015, Joonsoo Kim wrote:

> This patch uses is_via_compact_memory() to distinguish direct compaction.

When I think of "direct compaction", I think of compaction triggered for 
high-order allocations from the page allocator before direct reclaim.  
This is the opposite of being triggered for is_via_compact_memory().

> And it also reduces indentation on compaction_defer_reset
> by filtering failure case. There is no functional change.
> 
> Acked-by: Yaowei Bai <baiyaowei@...s.chinamobile.com>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> ---
>  mm/compaction.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index de3e1e7..01b1e5e 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1658,14 +1658,15 @@ static void __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
>  				!compaction_deferred(zone, cc->order))
>  			compact_zone(zone, cc);
>  
> -		if (cc->order > 0) {
> -			if (zone_watermark_ok(zone, cc->order,
> -						low_wmark_pages(zone), 0, 0))
> -				compaction_defer_reset(zone, cc->order, false);
> -		}
> -
>  		VM_BUG_ON(!list_empty(&cc->freepages));
>  		VM_BUG_ON(!list_empty(&cc->migratepages));
> +
> +		if (is_via_compact_memory(cc->order))
> +			continue;

This will be the third call to is_via_compact_memory() in this function.  
Maybe just do

	const bool sysctl = is_via_compact_memory(cc->order);

early in the function since it won't change during the iteration?  (And 
maybe get rid of that extra newline that already exists at the beginning 
of the iteration?

Otherwise:

Acked-by: David Rientjes <rientjes@...gle.com>
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