linux-kernel - Re: [PATCH 2/2] page-allocator: Maintain rolling count of pages to free from the PCP

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Message-ID: <20090828133631.GF5054@csn.ul.ie>
Date:	Fri, 28 Aug 2009 14:36:31 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	Pekka Enberg <penberg@...helsinki.fi>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] page-allocator: Maintain rolling count of pages to
	free from the PCP

On Fri, Aug 28, 2009 at 04:02:44PM +0300, Pekka Enberg wrote:
> Hi Mel,
> 
> On Fri, 2009-08-28 at 13:57 +0100, Mel Gorman wrote:
> > On Fri, Aug 28, 2009 at 03:16:34PM +0300, Pekka Enberg wrote:
> > > Hi Mel,
> > > 
> > > On Fri, Aug 28, 2009 at 11:44 AM, Mel Gorman<mel@....ul.ie> wrote:
> > > > -               page = list_entry(list->prev, struct page, lru);
> > > > -               /* have to delete it as __free_one_page list manipulates */
> > > > -               list_del(&page->lru);
> > > > -               trace_mm_page_pcpu_drain(page, 0, migratetype);
> > > > -               __free_one_page(page, zone, 0, migratetype);
> > > > +               do {
> > > > +                       page = list_entry(list->prev, struct page, lru);
> > > > +                       /* must delete as __free_one_page list manipulates */
> > > > +                       list_del(&page->lru);
> > > > +                       __free_one_page(page, zone, 0, migratetype);
> > > > +                       trace_mm_page_pcpu_drain(page, 0, migratetype);
> > > 
> > > This calls trace_mm_page_pcpu_drain() *after* __free_one_page(). It's
> > > probably not a good idea as __free_one_page() can alter the struct
> > > page in various ways.
> > > 
> > 
> > While true, does it alter the struct page in any way that matters?
> 
> Page flags and order are probably interesting for tracing?
> 

This is PCPU draining. The flags are already clear of any values of interest
and the order is always 0. I can follow up a fix-patch that reverses it just
in case but I don't think it makes a major difference?

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