linux-kernel - Re: [PATCH] Properly account for freed pages in free_pages_bulk() and when allocating high-order pages in buffered

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Date:	Tue, 28 Apr 2009 19:36:01 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Christoph Lameter <cl@...ux.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lin Ming <ming.m.lin@...el.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
Subject: Re: [PATCH] Properly account for freed pages in free_pages_bulk()
	and when allocating high-order pages in buffered_rmqueue()

On Tue, Apr 28, 2009 at 06:15:30PM +0100, Hugh Dickins wrote:
> On Tue, 28 Apr 2009, Mel Gorman wrote:
> > On Tue, Apr 28, 2009 at 12:37:22PM -0400, Christoph Lameter wrote:
> > > On Tue, 28 Apr 2009, Mel Gorman wrote:
> > > 
> > > > @@ -1151,6 +1151,7 @@ again:
> > > >  	} else {
> > > >  		spin_lock_irqsave(&zone->lock, flags);
> > > >  		page = __rmqueue(zone, order, migratetype);
> > > > +		__mod_zone_page_state(zone, NR_FREE_PAGES, -(1UL << order));
> > > >  		spin_unlock(&zone->lock);
> > > >  		if (!page)
> > > >  			goto failed;
> > > 
> > > __mod_zone_page_state takes an signed integer argument. Not sure what is
> > > won by the UL suffix here.
> > > 
> > 
> > Matches other call sites such as in __offline_isolated_pages(), habit when
> > using shifts like this and matches other locations, paranoia, doesn't hurt.
> 
> Well, not a big deal, but I'd say that it does hurt: by wasting people's
> time (mine!), wondering what that "UL" is for - I'd have had to ask, if
> Christoph hadn't cleared this up first (thank you).  And elsewhere,
> you're using an int << order to update NR_FREE_PAGES, so I don't see
> the consistency argument.
> 

Ok, I'll concede things are not super-consistent. In this case, I felt it
"didn't hurt" but I didn't take into account that it needs to be worked out
each time and I posted a second revision that should be clearer.

As an aside, in other places order changes from being signed in some places
to being unsigned in others. There is probably a pass in there just for
dealing with this sort of inconsistency.

Thanks

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