linux-kernel - Re: [PATCH v6 1/3] mm: introduce compaction and migration for virtio ballooned pages

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Message-ID: <20120810124649.GL10288@csn.ul.ie>
Date:	Fri, 10 Aug 2012 13:46:49 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Rafael Aquini <aquini@...hat.com>
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>,
	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Minchan Kim <minchan@...nel.org>
Subject: Re: [PATCH v6 1/3] mm: introduce compaction and migration for virtio
 ballooned pages

On Thu, Aug 09, 2012 at 12:12:19PM -0300, Rafael Aquini wrote:
> On Thu, Aug 09, 2012 at 11:48:36AM -0300, Rafael Aquini wrote:
> > Sure! 
> > what do you think of:
> > 
> > +/* putback_lru_page() counterpart for a ballooned page */
> > +void putback_balloon_page(struct page *page)
> > +{
> > +   lock_page(page);
> > +   if (!WARN_ON(!movable_balloon_page(page))) {
> > +           __putback_balloon_page(page);
> > +           put_page(page);
> > +   }
> > +   unlock_page(page);
> > +}
> >
> Or perhaps
>  
> +/* putback_lru_page() counterpart for a ballooned page */
> +void putback_balloon_page(struct page *page)
> +{
> +   if (!WARN_ON(!movable_balloon_page(page))) {
> +           lock_page(page);
> +           __putback_balloon_page(page);
> +           put_page(page);
> +           unlock_page(page);
> +   }
> +}

That should be fine. I find the WARN_ON construct odd to read but only
because it's unusual. It is more typical to see something like

if (WARN_ON(!movable_balooon_page(page)))
	return;

lock_page(page);
__putback_balloon_page(page);
put_page(page);
unlock_page(page);

but either works. Do not forget to update the caller of course.

Thanks.


-- 
Mel Gorman
SUSE Labs
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