Re: [PATCH 18/25] Do not disable interrupts in free_page_mlock()

Lee Schermerhorn
2009-04-22T14:42:28Z

On Wed, 2009-04-22 at 09:13 +0900, KOSAKI Motohiro wrote:
> (cc to Lee)
>
> > free_page_mlock() tests and clears PG_mlocked using locked versions of the
> > bit operations. If set, it disables interrupts to update counters and this
> > happens on every page free even though interrupts are disabled very shortly
> > afterwards a second time. This is wasteful.
> >
> > This patch splits what free_page_mlock() does. The bit check is still
> > made. However, the update of counters is delayed until the interrupts are
> > disabled and the non-lock version for clearing the bit is used. One potential
> > weirdness with this split is that the counters do not get updated if the
> > bad_page() check is triggered but a system showing bad pages is getting
> > screwed already.
>
> Looks good. thanks good improvement.
> I hope Lee also ack this.
>
> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
>
>
> -kosaki
>

Yes, this looks OK. If we're racing on a page that is being freed or,
as Mel notes, some other condition triggers bad_page(), we got bigger
problems than inaccurate statistics...

Acked-by: Lee Schermerhorn <lee.schermerhorn@hp.com>

>
> >
> > Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> > Reviewed-by: Christoph Lameter <cl@linux-foundation.org>
> > ---
> > mm/internal.h | 11 +++--------
> > mm/page_alloc.c | 8 +++++++-
> > 2 files changed, 10 insertions(+), 9 deletions(-)
> >
> > diff --git a/mm/internal.h b/mm/internal.h
> > index 987bb03..58ec1bc 100644
> > --- a/mm/internal.h
> > +++ b/mm/internal.h
> > @@ -157,14 +157,9 @@ static inline void mlock_migrate_page(struct page *newpage, struct page *page)
> > */
> > 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);
> > - }
> > + __ClearPageMlocked(page);
> > + __dec_zone_page_state(page, NR_MLOCK);
> > + __count_vm_event(UNEVICTABLE_MLOCKFREED);
> > }
> >
> > #else /* CONFIG_HAVE_MLOCKED_PAGE_BIT */
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index a1ca038..bf4b8d9 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -499,7 +499,6 @@ static inline void __free_one_page(struct page *page,
> >
> > static inline int free_pages_check(struct page *page)
> > {
> > - free_page_mlock(page);
> > if (unlikely(page_mapcount(page) |
> > (page->mapping != NULL) |
> > (page_count(page) != 0) |
> > @@ -556,6 +555,7 @@ static void __free_pages_ok(struct page *page, unsigned int order)
> > unsigned long flags;
> > int i;
> > int bad = 0;
> > + int clearMlocked = PageMlocked(page);
> >
> > for (i = 0 ; i < (1 << order) ; ++i)
> > bad += free_pages_check(page + i);
> > @@ -571,6 +571,8 @@ static void __free_pages_ok(struct page *page, unsigned int order)
> > kernel_map_pages(page, 1 << order, 0);
> >
> > local_irq_save(flags);
> > + if (unlikely(clearMlocked))
> > + free_page_mlock(page);
> > __count_vm_events(PGFREE, 1 << order);
> > free_one_page(page_zone(page), page, order,
> > get_pageblock_migratetype(page));
> > @@ -1018,6 +1020,7 @@ static void free_hot_cold_page(struct page *page, int cold)
> > struct zone *zone = page_zone(page);
> > struct per_cpu_pages *pcp;
> > unsigned long flags;
> > + int clearMlocked = PageMlocked(page);
> >
> > if (PageAnon(page))
> > page->mapping = NULL;
> > @@ -1033,7 +1036,10 @@ static void free_hot_cold_page(struct page *page, int cold)
> >
> > pcp = &zone_pcp(zone, get_cpu())->pcp;
> > local_irq_save(flags);
> > + if (unlikely(clearMlocked))
> > + free_page_mlock(page);
> > __count_vm_event(PGFREE);
> > +
> > if (cold)
> > list_add_tail(&page->lru, &pcp->list);
> > else
> > --
> > 1.5.6.5
> >