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



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