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

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Date:	Mon, 23 Feb 2009 13:44:18 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mel Gorman <mel@....ul.ie>
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, 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.

> > 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.

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