[dm-devel] [PATCH v2 0/4] brd: implement discard

[Gao Xiang]

On Thu, Sep 29, 2022 at 04:05:43PM -0400, Mikulas Patocka wrote:
> 
> 
> On Wed, 28 Sep 2022, Gao Xiang wrote:
> 
> > > Hi
> > > 
> > > Ramdisk DAX was there in the past, but it was removed in the kernel 4.15.
> > 
> > Hi Mikulas!
> > 
> > Thanks for pointing out! I didn't realize that, although I think if we really
> > use brd driver in production, enabling DAX support for brd is much better to
> > remove double caching so that ramdisk can become a real ramdisk for most
> > regular files.
> > 
> > I have no idea how other people think about ramdisk DAX, or brd is just a
> > stuff for testing only now.  If it behaves like this, sorry about the
> > noise.
> > 
> > Thanks,
> > Gao Xiang
> 
> Hi
> 
> See the message for the commit 7a862fbbdec665190c5ef298c0c6ec9f3915cf45 
> for the reason why it was removed.

I've already seen that commit after you told me, yet I think the reasons
listed inside are not fundamental reasons why ramdisk cannot support DAX
in principle (although I know there are issues as listed to handle.)

IMHO, reserving ZONE_DEVICE memory to emulate pmem for ramdisk DAX-like
use is inflexible on my side since currently such reserved memory cannot
be used for other uses later even the ramdisk actually use little space
in practice regardless of its capacity.

Thanks,
Gao Xiang

> 
> Mikulas