On Tue, Sep 27, 2022 at 10:09:04AM -0400, Mikulas Patocka wrote:

On Wed, 21 Sep 2022, Gao Xiang wrote:

quoted

On Tue, Sep 20, 2022 at 01:52:38PM -0400, Mikulas Patocka wrote:

quoted

Hi

Here I'm sending second version of the brd discard patches.

That is quite interesting.

btw, something out of topic, I once had some preliminary attempt
to add DAX support to brd since brd works as ramdisk and brd-dax
could have the following benefits:

 - DAX can be tested without PMEM devices;
 - ramdisk fses can be accessed without double page cache;
 - initrd use cases then can work well without extra page cache
   and maybe it can perform better than initramfs (without unpack
   process).

I wrote some hack stuff but don't have more time working on it...
https://git.kernel.org/pub/scm/linux/kernel/git/xiang/linux.git/log/?h=erofs/initrd-fsdax

I'm not sure if others are interested in topic though.

It would be helpful to get rid of all brd page->index use cases
first.

Thanks,
Gao Xiang

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

Mikulas