Re: dm overlaybd: targets mapping OverlayBD image

[Du Rui]

> Block drivers has nothing to do on filesystem page cache stuffs, also
> currently your approach has nothing to do with pmem stuffs (If you must
> mention "DAX" to proposal your "page cache sharing", please _here_
> write down your detailed design first and explain how it could work to
> ours if you really want to do.)

We have already done experiments (by virtio pmem), to make virtual PMEM
device in QEMU, make guest vm sharing only one memory mapping on host,
with filesystem that supports DAX. In guest vm, fs keeps no page cache,
maybe "sharing pagecache" is not such accurate description, but sharing
memory pages on host can do prevent making duplicated pagecache pages in
VMs.

Please make sure that you have already understood that dm-overlaybd are
for GENERIC purpose. It is NOT a special design for container, and have
nothing related to filesystem implementations.