linux-kernel - Re: [PATCH v11 3/7] mm: introduce a common interface for balloon pages mobility

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Date:	Wed, 7 Nov 2012 19:34:28 -0200
From:	Rafael Aquini <aquini@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mel@....ul.ie>,
	Andi Kleen <andi@...stfloor.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Minchan Kim <minchan@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v11 3/7] mm: introduce a common interface for balloon
 pages mobility

On Wed, Nov 07, 2012 at 01:02:07PM -0800, Andrew Morton wrote:
> On Wed,  7 Nov 2012 01:05:50 -0200
> Rafael Aquini <aquini@...hat.com> wrote:
> 
> > Memory fragmentation introduced by ballooning might reduce significantly
> > the number of 2MB contiguous memory blocks that can be used within a guest,
> > thus imposing performance penalties associated with the reduced number of
> > transparent huge pages that could be used by the guest workload.
> > 
> > This patch introduces a common interface to help a balloon driver on
> > making its page set movable to compaction, and thus allowing the system
> > to better leverage the compation efforts on memory defragmentation.
> 
> 
> mm/migrate.c: In function 'unmap_and_move':
> mm/migrate.c:899: error: 'COMPACTBALLOONRELEASED' undeclared (first use in this function)
> mm/migrate.c:899: error: (Each undeclared identifier is reported only once
> mm/migrate.c:899: error: for each function it appears in.)
> 
> You've been bad - you didn't test with your feature disabled. 
> Please do that.  And not just compilation testing.
>

Gasp... Shame on me, indeed. balloon_event_count() was a macro and I had it
tested a couple of review rounds earlier. You requested me to get rid of
preprocessor pirotech, and I did but I miserably failed on re-testing it.
 
I'm pretty sure Santa is not going to visit me this year.

Do you want me to resubmit this?

> 
> We can fix this one with a sucky macro.  I think that's better than
> unconditionally defining the enums.
> 
> --- a/include/linux/balloon_compaction.h~mm-introduce-a-common-interface-for-balloon-pages-mobility-fix
> +++ a/include/linux/balloon_compaction.h
> @@ -207,10 +207,8 @@ static inline gfp_t balloon_mapping_gfp_
>  	return GFP_HIGHUSER;
>  }
>  
> -static inline void balloon_event_count(enum vm_event_item item)
> -{
> -	return;
> -}
> +/* A macro, to avoid generating references to the undefined COMPACTBALLOON* */
> +#define balloon_event_count(item) do { } while (0)
>  
>  static inline bool balloon_compaction_check(void)
>  {
> 
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