On 23.08.21 16:05, Gerald Schaefer wrote:
On Fri, 20 Aug 2021 07:43:40 +0200
Christoph Hellwig <hch@xxxxxx> wrote:
Hi all,
looking at the recent ZONE_DEVICE related changes we still have a
horrible maze of different code paths. I already suggested to
depend on ARCH_HAS_PTE_SPECIAL for ZONE_DEVICE there, which all modern
architectures have anyway. But the other odd special case is
CONFIG_FS_DAX_LIMITED which is just used for the xpram driver. Does
this driver still see use? If so can we make it behave like the
other DAX drivers and require a pgmap? I think the biggest missing
part would be to implement ARCH_HAS_PTE_DEVMAP for s390.
Puh, yes, that seems to be needed in order to enable ZONE_DEVICE, and
then we could use devm_memremap_pages(), at least that was my plan
some time ago. However, either the ARCH_HAS_PTE_DEVMAP dependency
is new, or I overlooked it before, but we do not have any free bits
in the pte left, so this is not going to work.
Would it strictly be necessary to implement ZONE_DEVICE, or would
it be enough if we would use e.g. add_memory() instead of just
adding the DCSS memory directly to the kernel mapping via
vmem_add_mapping()? That way we might at least get the struct pages,
but somehow it doesn't feel completely right.
add_memory() is for adding system RAM. I don't think that's what you
want in the case of DCSS. Supporting ZONE_DEVICE cleanly would be ideal.
--
Thanks,
David / dhildenb
