Re: [PATCH] backing dev unplugging

Christophe Saout
2004-03-11T13:11:32Z

Am Do, den 11.03.2004 schrieb Jens Axboe um 13:22:

> > If we were out of memory the buffers were allocated from a mempool and I
> > want to get it out as soon as possible. If we are OOM the write will
> > most likely be the VM trying to free some memory and it would be
> > counterproductive to wait. It is not unlikely that we are the only
> > writer to that disk so there's a chance that the queue is not congested.
>
> Because it wasn't right, like most of those blk_run_queues(). The vm
> should get things going, you basically just want to take a little nap
> and retry. The idea with a small wait is to allow io to make some
> progress, you gain nothing retrying right away (except wasting CPU
> spinning). It might want to be 1 instead of HZ/100, though. I doubt it
> would make much difference, since it's an OOM condition.

Well, okay. You're right then. I think the wait is unnecessary because
the next thing that the code tries to do is to allocate a new page,
waiting allowed and the VM will run the queue and wait itself. So if you
think it's safe you can even remove it.

Thanks.