On Fri, Sep 17, 2021 at 01:53:33PM +0100, Christoph Hellwig wrote:
> On Thu, Sep 16, 2021 at 11:40:28AM -0700, Dan Williams wrote:
> > > That was my gut feeling. If everyone feels 100% comfortable with
> > > zeroingas the mechanism to clear poisoning I'll cave in. The most
> > > important bit is that we do that through a dedicated DAX path instead
> > > of abusing the block layer even more.
> >
> > ...or just rename dax_zero_page_range() to dax_reset_page_range()?
> > Where reset == "zero + clear-poison"?
>
> I'd say that naming is more confusing than overloading zero.
How about dax_zeroinit_range() ?
To go with its fallocate flag (yeah I've been too busy sorting out -rc1
regressions to repost this) FALLOC_FL_ZEROINIT_RANGE that will reset the
hardware (whatever that means) and set the contents to the known value
zero.
Userspace usage model:
void handle_media_error(int fd, loff_t pos, size_t len)
{
/* yell about this for posterior's sake */
ret = fallocate(fd, FALLOC_FL_ZEROINIT_RANGE, pos, len);
/* yay our disk drive / pmem / stone table engraver is online */
}
> > > I'm really worried about both patartitions on DAX and DM passing through
> > > DAX because they deeply bind DAX to the block layer, which is just a bad
> > > idea. I think we also need to sort that whole story out before removing
> > > the EXPERIMENTAL tags.
> >
> > I do think it was a mistake to allow for DAX on partitions of a pmemX
> > block-device.
> >
> > DAX-reflink support may be the opportunity to start deprecating that
> > support. Only enable DAX-reflink for direct mounting on /dev/pmemX
> > without partitions (later add dax-device direct mounting),
>
> I think we need to fully or almost fully sort this out.
>
> Here is my bold suggestions:
>
> 1) drop no drop the EXPERMINTAL on the current block layer overload
> at all
I don't understand this.
> 2) add direct mounting of the nvdimm namespaces ASAP. Because all
> the filesystem currently also need the /dev/pmem0 device add a way
> to open the block device by the dax_device instead of our current
> way of doing the reverse
> 3) deprecate DAX support through block layer mounts with a say 2 year
> deprecation period
> 4) add DAX remapping devices as needed
What devices are needed? linear for lvm, and maybe error so we can
actually test all this stuff?
> I'll volunteer to write the initial code for 2). And I think we should
> not allow DAX+reflink on the block device shim at all.
/me has other questions about daxreflink, but I'll ask them on shiyang's
thread.
--D
