Re: [Lsf-pc] [LSF/MM TOPIC] Remote access to pmem on storage targets

[Dave Chinner <david@fromorbit.com>]

On Tue, Jan 26, 2016 at 10:58:44AM -0500, Chuck Lever wrote:
> It is not going to be like the well-worn paradigm that
> involves a page cache on the storage target backed by
> slow I/O operations. The protocol layers on storage
> targets need a way to discover memory addresses of
> persistent memory that will be used as source/sink
> buffers for RDMA operations.
> 
> And making data durable after a write is going to need
> some thought. So I believe some new plumbing will be
> necessary.

Haven't we already solve this for the pNFS file driver that XFS
implements? i.e. these export operations:

        int (*get_uuid)(struct super_block *sb, u8 *buf, u32 *len, u64 *offset);
        int (*map_blocks)(struct inode *inode, loff_t offset,
                          u64 len, struct iomap *iomap,
                          bool write, u32 *device_generation);
        int (*commit_blocks)(struct inode *inode, struct iomap *iomaps,
                             int nr_iomaps, struct iattr *iattr);

so mapping/allocation of file offset to sector mappings, which can
then trivially be used to grab the memory address through the bdev
->direct_access method, yes?

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com