__lock_page calls run_task_queue(&tq_disk) unecessarily?

[Marcelo Tosatti]

Hi Linus,

Take a look at __lock_page:

static void __lock_page(struct page *page)
{
        struct task_struct *tsk = current;
        DECLARE_WAITQUEUE(wait, tsk);

        add_wait_queue_exclusive(&page->wait, &wait);
        for (;;) {
                sync_page(page);
                set_task_state(tsk, TASK_UNINTERRUPTIBLE);
                if (PageLocked(page)) {
                        run_task_queue(&tq_disk);
                        schedule();
                        continue;
                }
                if (!TryLockPage(page))
                        break;
        }
        tsk->state = TASK_RUNNING;
        remove_wait_queue(&page->wait, &wait);
}

Af a process sleeps in __lock_page, sync_page() will be called even if the
page is already unlocked. (block_sync_page(), the sync_page routine for
generic block based filesystem calls run_task_queue(&tq_disk)).

I don't see any problem if we remove the run_task_queue(&tq_disk) and put
sync_page(page) there instead, removing the other sync_page(page) at the
beginning of the loop.

Comments?