Re: [PATCH V2 1/1] pmem: set QUEUE_FLAG_NOWAIT

[Jeff Moyer <jmoyer@redhat.com>]

Christoph Hellwig <hch@lst.de> writes:

> Given that pmem simply loops over an arbitrarily large bio I think
> we also need a threshold for which to allow nowait I/O.  While it
> won't block for giant I/Os, doing all of them in the submitter
> context isn't exactly the idea behind the nowait I/O.
>
> I'm not really sure what a good theshold would be, though.

There's no mention of the latency of the submission side in the
documentation for RWF_NOWAIT.  The man page says "Do not wait for data
which is not immediately available."  Data in pmem *is* immediately
available.  If we wanted to enforce a latency threshold for submission,
it would have to be configurable and, ideally, a part of the API.  I
don't think it's something we should even try to guarantee, though,
unless application writers are asking for it.

So, I think with the change to return -EAGAIN for writes to poisoned
memory, this patch is probably ok.

Chaitanya, could you send a v2?

Thanks,
Jeff