linux-kernel - Re: [PATCH 17/25] Do not call get_pageblock

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Message-ID: <20090421161215.GD29083@csn.ul.ie>
Date:	Tue, 21 Apr 2009 17:12:16 +0100
From:	Mel Gorman <mel@....ul.ie>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	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>,
	Lin Ming <ming.m.lin@...el.com>,
	Zhang Yanmin <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 17/25] Do not call get_pageblock_migratetype() more
	than necessary

On Tue, Apr 21, 2009 at 08:03:10PM +0900, KOSAKI Motohiro wrote:
> > get_pageblock_migratetype() is potentially called twice for every page
> > free. Once, when being freed to the pcp lists and once when being freed
> > back to buddy. When freeing from the pcp lists, it is known what the
> > pageblock type was at the time of free so use it rather than rechecking.
> > In low memory situations under memory pressure, this might skew
> > anti-fragmentation slightly but the interference is minimal and
> > decisions that are fragmenting memory are being made anyway.
> > 
> > Signed-off-by: Mel Gorman <mel@....ul.ie>
> > Reviewed-by: Christoph Lameter <cl@...ux-foundation.org>
> > ---
> >  mm/page_alloc.c |   16 ++++++++++------
> >  1 files changed, 10 insertions(+), 6 deletions(-)
> > 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index c57c602..a1ca038 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -456,16 +456,18 @@ static inline int page_is_buddy(struct page *page, struct page *buddy,
> >   */
> >  
> >  static inline void __free_one_page(struct page *page,
> > -		struct zone *zone, unsigned int order)
> > +		struct zone *zone, unsigned int order,
> > +		int migratetype)
> >  {
> >  	unsigned long page_idx;
> >  	int order_size = 1 << order;
> > -	int migratetype = get_pageblock_migratetype(page);
> >  
> >  	if (unlikely(PageCompound(page)))
> >  		if (unlikely(destroy_compound_page(page, order)))
> >  			return;
> >  
> > +	VM_BUG_ON(migratetype == -1);
> > +
> >  	page_idx = page_to_pfn(page) & ((1 << MAX_ORDER) - 1);
> >  
> >  	VM_BUG_ON(page_idx & (order_size - 1));
> > @@ -534,17 +536,18 @@ static void free_pages_bulk(struct zone *zone, int count,
> >  		page = list_entry(list->prev, struct page, lru);
> >  		/* have to delete it as __free_one_page list manipulates */
> >  		list_del(&page->lru);
> > -		__free_one_page(page, zone, order);
> > +		__free_one_page(page, zone, order, page_private(page));
> >  	}
> >  	spin_unlock(&zone->lock);
> 
> looks good.
> 	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> 
> 
> btw, I can't review rest patch today. I plan to do that tommorow, sorry.
> 

No problem. Thanks a million for the work you've done so far. It was a
big help and you caught a fair few problems in there.

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