Re: [PATCH 1/2] sched/wait: Break up long wake list walk

[Peter Zijlstra <peterz@infradead.org>]

On Tue, Aug 22, 2017 at 01:42:13PM -0700, Linus Torvalds wrote:
> +void wait_on_page_bit_or_yield(struct page *page, int bit_nr)
> +{
> +	if (PageWaiters(page)) {
> +		yield();
> +		return;
> +	}
> +	wait_on_page_bit(page, bit_nr);
> +}

So _the_ problem with yield() is when you hit this with a RT task it
will busy spin and possibly not allow the task that actually has the
lock to make progress at all.

So ideally there'd be a timeout or other limit on the amount of yield().

This being bit-spinlocks leaves us very short on state to play with
though :/

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>