linux-kernel - Re: [PATCH] mm: Warn once when a page is freed with PG

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Message-ID: <20090724125910.GB18074@csn.ul.ie>
Date:	Fri, 24 Jul 2009 13:59:10 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	kosaki.motohiro@...fujitsu.com, maximlevitsky@...il.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Lee.Schermerhorn@...com, penberg@...helsinki.fi,
	jirislaby@...il.com
Subject: Re: [PATCH] mm: Warn once when a page is freed with PG_mlocked set
	V2

On Fri, Jul 24, 2009 at 02:00:04PM +0200, Johannes Weiner wrote:
> On Fri, Jul 24, 2009 at 11:36:56AM +0100, Mel Gorman wrote:
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index b8283e8..d3d0707 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -488,6 +488,11 @@ static inline void __free_one_page(struct page *page,
> >   */
> >  static inline void free_page_mlock(struct page *page)
> >  {
> > +	WARN_ONCE(1, KERN_WARNING
> > +		"Page flag mlocked set for process %s at pfn:%05lx\n"
> > +		"page:%p flags:%#lx\n",
> > +		current->comm, page_to_pfn(page),
> > +		page, page->flags|__PG_MLOCKED);
> 
> I don't think printing page->flags is all too useful after they have
> been cleared by free_pages_check().
> 

I considered that and was going to drop them. Then I remembered that the
node and zone linkages can also be encoded in the flags and conceivably they
could still be useful so I left it.

> But it's probably a reasonable trade-off for not having it in the
> fast-path.
> 
> Acked-by: Johannes Weiner <hannes@...xchg.org>
> 

Thanks

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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