Re: [PATCH 15/20] Do not disable interrupts in free_page_mlock()

Peter Zijlstra
2009-02-23T12:44:44Z

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.