On 05/15, Peter Zijlstra wrote:
>
> So I suppose I'm failing to see the problem with something like:
Yeeees, I was thinking about something like this too ;)
> static inline void lock_page(struct page *page)
> {
> if (!trylock_page(page))
> __lock_page(page);
> }
>
> static inline void unlock_page(struct page *page)
> {
> clear_bit_unlock(&page->flags, PG_locked);
> if (PageWaiters(page))
> __unlock_page();
> }
but in this case we need mb() before PageWaiters(), I guess.
> void __lock_page(struct page *page)
> {
> struct wait_queue_head_t *wqh = page_waitqueue(page);
> DEFINE_WAIT_BIT(wait, &page->flags, PG_locked);
>
> spin_lock_irq(&wqh->lock);
> if (!PageWaiters(page))
> SetPageWaiters(page);
>
> wait.flags |= WQ_FLAG_EXCLUSIVE;
> preempt_disable();
why?
> do {
> if (list_empty(&wait->task_list))
> __add_wait_queue_tail(wqh, &wait);
>
> set_current_state(TASK_UNINTERRUPTIBLE);
>
> if (test_bit(wait.key.bit_nr, wait.key.flags)) {
> spin_unlock_irq(&wqh->lock);
> schedule_preempt_disabled();
> spin_lock_irq(&wqh->lock);
OK, probably to avoid the preemption before schedule(). Still can't
undestand why this makes sense, but in this case it would be better
to do disable/enable under "if (test_bit())" ?
Of course, this needs more work for lock_page_killable(), but this
should be simple.
Oleg.
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