Re: [PATCH] [9/20] Add blk_kmalloc/blk_alloc_pages

[FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>]

On Mon, 17 Mar 2008 22:34:22 +0100
Andi Kleen <andi@firstfloor.org> wrote:

> > Look further down in the email, queue_bounce_to_mask() or whatever you
> > would want to call it. As also written there, the PRINCIPLE is the same.
> > And that is that exporting a to_allocator_mask() helper is a lot saner
> > than exporting an allocator api tied to the queue.
> > 
> > Can we get over this, please?
> 
> Ok it would have helped if you had explained why it is saner, but I 
> bow to your superior experience on block layer issues.
> 
> The only open issue is right now if it isn't better to go back
> for automatic bouncing for SCSI scan and the other users. Do you
> have an opinion on that too? If you have one can you please convince
> James of it too.

There are other things that don't want the automatic bouncing; sg, st,
and osst.

Your patches remove unchecked_isa_dma in them and Boaz said that they
are fine since they get bounced anyway, however, it's not correct.

As Doug said in another thread (about your patch to change GFP_ATOMIC
to GFP_KERNEL in sg), they try to avoid waiting for a long time and
want an early failure (though they are not complete; can't avoid non
unchecked_isa_dma bouncing) .

We can change the bounce path in that way, but I think it's better if
they can allocate memory that will not get bounced.