On Tue, May 13, 2014 at 10:45:50AM +0100, Mel Gorman wrote:
> diff --git a/mm/filemap.c b/mm/filemap.c
> index c60ed0f..d81ed7d 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -241,15 +241,15 @@ void delete_from_page_cache(struct page *page)
> }
> EXPORT_SYMBOL(delete_from_page_cache);
>
> -static int sleep_on_page(void *word)
> +static int sleep_on_page(void)
> {
> - io_schedule();
> + io_schedule_timeout(HZ);
> return 0;
> }
>
> -static int sleep_on_page_killable(void *word)
> +static int sleep_on_page_killable(void)
> {
> - sleep_on_page(word);
> + sleep_on_page();
> return fatal_signal_pending(current) ? -EINTR : 0;
> }
>
I've got a patch from NeilBrown that conflicts with this, shouldn't be
hard to resolve though.
> @@ -680,30 +680,105 @@ static wait_queue_head_t *page_waitqueue(struct page *page)
> return &zone->wait_table[hash_ptr(page, zone->wait_table_bits)];
> }
>
> -static inline void wake_up_page(struct page *page, int bit)
> +static inline wait_queue_head_t *clear_page_waiters(struct page *page)
> {
> - __wake_up_bit(page_waitqueue(page), &page->flags, bit);
> + wait_queue_head_t *wqh = NULL;
> +
> + if (!PageWaiters(page))
> + return NULL;
> +
> + /*
> + * Prepare to clear PG_waiters if the waitqueue is no longer
> + * active. Note that there is no guarantee that a page with no
> + * waiters will get cleared as there may be unrelated pages
> + * sleeping on the same page wait queue. Accurate detection
> + * would require a counter. In the event of a collision, the
> + * waiter bit will dangle and lookups will be required until
> + * the page is unlocked without collisions. The bit will need to
> + * be cleared before freeing to avoid triggering debug checks.
> + *
> + * Furthermore, this can race with processes about to sleep on
> + * the same page if it adds itself to the waitqueue just after
> + * this check. The timeout in sleep_on_page prevents the race
> + * being a terminal one. In effect, the uncontended and non-race
> + * cases are faster in exchange for occasional worst case of the
> + * timeout saving us.
> + */
> + wqh = page_waitqueue(page);
> + if (!waitqueue_active(wqh))
> + ClearPageWaiters(page);
> +
> + return wqh;
> +}
This of course is properly disgusting, but my brain isn't working right
on 4 hours of sleep, so I'm able to suggest anything else.
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