Re: [PATCH 0/5] bio: Direct IO: convert to pin_user_pages_fast()

[John Hubbard]

On 8/24/20 6:54 PM, Al Viro wrote:

On Fri, Aug 21, 2020 at 09:20:54PM -0700, John Hubbard wrote:

Direct IO behavior:

     ITER_IOVEC:
         pin_user_pages_fast();
         break;

     ITER_KVEC:    // already elevated page refcount, leave alone
     ITER_BVEC:    // already elevated page refcount, leave alone
     ITER_PIPE:    // just, no :)

Why?  What's wrong with splice to O_DIRECT file?

Oh! I'll take a look. Is this the fs/splice.c stuff?  I ruled this out early
mainly based on Christoph's comment in [1] ("ITER_PIPE is rejected іn the
direct I/O path"), but if it's supportable then I'll hook it up.

(As you can see, I'm still very much coming up to speed on the various things
that invoke iov_iter_get_pages*().)

[1] https://lore.kernel.org/kvm/20190724061750.ga19...@infradead.org/

thanks,
--
John Hubbard
NVIDIA