linux-kernel - Re: [PATCH 15/20] Do not disable interrupts in free_page

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Message-ID: <20090223142505.GI6740@csn.ul.ie>
Date:	Mon, 23 Feb 2009 14:25:06 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Peter Zijlstra <peterz@...radead.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>,
	Christoph Lameter <cl@...ux-foundation.org>,
	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>
Subject: Re: [PATCH 15/20] Do not disable interrupts in free_page_mlock()

On Mon, Feb 23, 2009 at 01:44:18PM +0100, Peter Zijlstra wrote:
> On Mon, 2009-02-23 at 12:23 +0000, Mel Gorman wrote:
> > On Mon, Feb 23, 2009 at 10:19:00AM +0100, Peter Zijlstra wrote:
> > > On Sun, 2009-02-22 at 23:17 +0000, Mel Gorman wrote:
> 
> > > >  static inline void free_page_mlock(struct page *page)
> > > >  {
> > > > -	if (unlikely(TestClearPageMlocked(page))) {
> > > > -		unsigned long flags;
> > > > -
> > > > -		local_irq_save(flags);
> > > > -		__dec_zone_page_state(page, NR_MLOCK);
> > > > -		__count_vm_event(UNEVICTABLE_MLOCKFREED);
> > > > -		local_irq_restore(flags);
> > > > -	}
> > > > +	__dec_zone_page_state(page, NR_MLOCK);
> > > > +	__count_vm_event(UNEVICTABLE_MLOCKFREED);
> > > >  }
> > > 
> > > Its not actually clearing PG_mlocked anymore, so the name is now a tad
> > > misleading.
> > > 
> > 
> > Really? I see the following
> 
> > So there is a PG_mlocked bit once UNEVITABLE_LRU is set which was the
> > case on the tests I was running. I'm probably missing something silly.
> 
> What I was trying to say was that free_page_mlock() doesn't change the
> page-state after your change, hence the 'free' part of its name is
> misleading.
> 

Ah right. As you pointed out on mail, the newer version clears the bit
again so while the name was misleading, it's sortof ok again now. Mind you,
it's not freeing a page as such. A name like account_freed_mlock() might be
better. As it is only used in page_alloc.c, it could also be taken out of
the header file altogether.

> > > That said, since we're freeing the page, there ought to not be another
> > > reference to the page, in which case it appears to me we could safely
> > > use the unlocked variant of TestClear*().
> > > 
> > 
> > Regrettably, unlocked variants do not appear to be defined as such but
> > the following should do the job, right? It applies on top of the current
> > change.
> > 
> > diff --git a/mm/internal.h b/mm/internal.h
> > index b52bf86..7f775a1 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -155,6 +155,7 @@ static inline void mlock_migrate_page(struct page *newpage, struct page *page)
> >   */
> >  static inline void free_page_mlock(struct page *page)
> >  {
> 	VM_BUG_ON(!PageMlocked(page)); ?
> 
> > +	__ClearPageMlocked(page);
> >  	__dec_zone_page_state(page, NR_MLOCK);
> >  	__count_vm_event(UNEVICTABLE_MLOCKFREED);
> >  }
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index edac673..8bd0533 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -580,7 +580,7 @@ static void __free_pages_ok(struct page *page, unsigned int order,
> >  	unsigned long flags;
> >  	int i;
> >  	int bad = 0;
> > -	int clearMlocked = TestClearPageMlocked(page);
> > +	int clearMlocked = PageMlocked(page);
> >  
> >  	for (i = 0 ; i < (1 << order) ; ++i)
> >  		bad += free_pages_check(page + i);
> > @@ -1040,7 +1040,7 @@ static void free_pcp_page(struct page *page)
> >  	struct per_cpu_pages *pcp;
> >  	unsigned long flags;
> >  	int migratetype;
> > -	int clearMlocked = TestClearPageMlocked(page);
> > +	int clearMlocked = PageMlocked(page);
> >  
> >  	if (PageAnon(page))
> >  		page->mapping = NULL;
> 
> Right, that should do.
> 

Nice, thanks.

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