Re: [RFC][PATCH] Vector read/write support for NFS (DIO) client

[Christoph Hellwig <hch@infradead.org>]

On Tue, Apr 12, 2011 at 11:49:29AM -0400, Trond Myklebust wrote:
> Your approach goes in the direction of further special-casing O_DIRECT
> in the NFS client. I'd like to move away from that and towards
> integration with the ordinary read/write codepaths so that aside from
> adding request coalescing, we can also enable pNFS support.

What is the exact plan?  Split the direct I/O into two passes, one
to lock down the user pages and then a second one to send the pages
over the wire, which is shared with the writeback code?  If that's
the case it should naturally allow plugging in a scheme like Badari
to send pages from different iovecs in a single on the wire request -
after all page cache pages are non-continuous in virtual and physical
memory, too.

When do you plan to release your read/write code re-write?  If it's
not anytime soon how is applying Badari's patch going to hurt?  Most
of it probably will get reverted with a complete rewrite, but at least
the logic to check which direct I/O iovecs can coalesced would stay
in the new world order.