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

Pekka Enberg
2009-04-21T07:54:20Z

On Mon, 2009-04-20 at 23:20 +0100, Mel Gorman wrote:
> 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.
>
> Signed-off-by: Mel Gorman <mel@csn.ul.ie>
> Reviewed-by: Christoph Lameter <cl@linux-foundation.org>

Reviewed-by: Pekka Enberg <penberg@cs.helsinki.fi>

> ---
> 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);
> - }

Maybe add a VM_BUG_ON(!PageMlocked(page))?

> + __ClearPageMlocked(page);
> + __dec_zone_page_state(page, NR_MLOCK);
> + __count_vm_event(UNEVICTABLE_MLOCKFREED);
> }
>
> #else /* CONFIG_HAVE_MLOCKED_PAGE_BIT */