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

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Date:	Thu, 26 Nov 2015 10:59:50 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	David Rientjes <rientjes@...gle.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
Subject: Re: [PATCH v2] mm/compaction: __compact_pgdat() code cleanuup

On Wed, Nov 25, 2015 at 02:45:15AM -0800, David Rientjes wrote:
> 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().

Okay. Will change it.

> 
> > 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?

I don't it's better. is_via_compact_memory() already express it's
meaning perfectly and no overhead here. Introducing extra variable
would confuse reader more than commonly used is_via_compact_memory().

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

Thanks.


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