Re: [PATCH v3 0/2] iov_iter: allow iov_iter_get_pages_alloc to allocate more pages per call

[Christoph Hellwig]

On Thu, Feb 02, 2017 at 08:00:52AM -0500, Jeff Layton wrote:
> Yeah, that might work. You could kmalloc the buffer array according to
> the maxsize value. For small ones we could even consider using an on-
> stack buffer.

For the block direct I/O code we defintively want to avoid any
allocations for small I/O a that shows up in the performance numbers.
And we'd like to reuse the on-stack bio_vec so that the defintion of
a small I/O can be as big as possible without blowing up the stack.