linux-kernel - Re: [PATCH 26/35] Use the per-cpu allocator for orders up to PAGE_ALLOC_COSTLY

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Date:	Mon, 16 Mar 2009 16:47:36 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Linux Memory Management List <linux-mm@...ck.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Rik van Riel <riel@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Johannes Weiner <hannes@...xchg.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>
Subject: Re: [PATCH 26/35] Use the per-cpu allocator for orders up to
	PAGE_ALLOC_COSTLY_ORDER

On Mon, Mar 16, 2009 at 12:26:07PM -0400, Christoph Lameter wrote:
> On Mon, 16 Mar 2009, Mel Gorman wrote:
> 
> > -static void free_hot_cold_page(struct page *page, int cold)
> > +static void free_hot_cold_page(struct page *page, int order, int cold)
> >  {
> >  	struct zone *zone = page_zone(page);
> >  	struct per_cpu_pages *pcp;
> >  	unsigned long flags;
> >  	int clearMlocked = PageMlocked(page);
> >
> > +	/* SLUB can return lowish-order compound pages that need handling */
> > +	if (order > 0 && unlikely(PageCompound(page)))
> > +		if (unlikely(destroy_compound_page(page, order)))
> > +			return;
> > +
> 
> Isnt that also true for stacks and generic network objects ==- 8k?
> 

I think they are vanilla high-order pages, not compound pages.

> >  again:
> >  	cpu  = get_cpu();
> > -	if (likely(order == 0)) {
> > +	if (likely(order <= PAGE_ALLOC_COSTLY_ORDER)) {
> >  		struct per_cpu_pages *pcp;
> > +		int batch;
> > +		int delta;
> >
> >  		pcp = &zone_pcp(zone, cpu)->pcp;
> > +		batch = max(1, pcp->batch >> order);
> >  		local_irq_save(flags);
> >  		if (!pcp->count) {
> > -			pcp->count = rmqueue_bulk(zone, 0,
> > -					pcp->batch, &pcp->list, migratetype);
> > +			delta = rmqueue_bulk(zone, order, batch,
> > +					&pcp->list, migratetype);
> > +			bulk_add_pcp_page(pcp, order, delta);
> >  			if (unlikely(!pcp->count))
> >  				goto failed;
> 
> The pcp adds a series of order N pages if an order N alloc occurs and the
> queue is empty?
> 

Nope, that would be bad. The calculation of batch is made above and is

batch = max(1, pcp->batch >> order);

so order is taken into account when deciding how many pages to allocate.

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