linux-kernel - Re: [PATCH 10/10] mm, page_alloc: Only enforce watermarks for order-0 allocations

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Message-Id: <20150930133704.b204cc34b5fac8ab8f0780c3@linux-foundation.org>
Date:	Wed, 30 Sep 2015 13:37:04 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mgorman@...hsingularity.net>
Cc:	Vlastimil Babka <vbabka@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Michal Hocko <mhocko@...nel.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 10/10] mm, page_alloc: Only enforce watermarks for
 order-0 allocations

On Wed, 30 Sep 2015 16:12:34 +0100 Mel Gorman <mgorman@...hsingularity.net> wrote:

> On Wed, Sep 30, 2015 at 04:17:44PM +0200, Vlastimil Babka wrote:
> > >---
> > >  mm/page_alloc.c | 11 ++++++++---
> > >  1 file changed, 8 insertions(+), 3 deletions(-)
> > >
> > >diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > >index 25731624d734..fedec98aafca 100644
> > >--- a/mm/page_alloc.c
> > >+++ b/mm/page_alloc.c
> > >@@ -2332,7 +2332,7 @@ static bool __zone_watermark_ok(struct zone *z, unsigned int order,
> > >  {
> > >  	long min = mark;
> > >  	int o;
> > >-	const bool alloc_harder = (alloc_flags & ALLOC_HARDER);
> > >+	const int alloc_harder = (alloc_flags & ALLOC_HARDER);
> > 
> > How bout the !!(alloc_flags & ALLOC_HARDER) conversion to bool? Unless it
> > forces to make the compiler some extra work...
> > 
> 
> Some people frown upon that trick as being obscure when it's not unnecessary
> and a modern compiler is meant to get it right. The int is clear and
> obvious in this context so I just went with it.

Yes, the !!  does generate extra code.  It doesn't seem worthwhile
overhead for a tiny cosmetic thing.
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