From: Christoph Hellwig [mailto:email@example.com]
On Sun, Jan 22, 2017 at 06:19:24PM +0000, Matthew Wilcox wrote:
> No, I mean a network filesystem like 9p or cifs or nfs. If the memcpy
> is supposed to be performed by the backing device
struct backing_dev has no relation to the DAX code. Even more so what's
the point of doing a DAXish memcpy in that case? If we buffer in
memory for network I/O we should just use the page cache.
Oh, I didn't mean a 'struct backing_dev'. I meant that, conceptually, there
is no driver for the filesystem to call. Here's the architecture that I'm trying
to work with:
Two guests on the same physical machine (or a guest and a host) have access to the same
set of physical addresses. This might be an NV-DIMM, or it might just be DRAM (for the
purposes of reducing guest overhead). The network filesystem has been enhanced with a
call to allow the client to ask the server "What is the physical address for this
range of bytes in this file?"
We don't want to use the guest pagecache here. That's antithetical to the second
usage, and it's inefficient for the first usage.