Re: can we finally kill off CONFIG_FS_DAX_LIMITED

Dan Williams
2021-08-20T15:42:06Z

[ add Gerald and Joao ]

On Thu, Aug 19, 2021 at 10:44 PM Christoph Hellwig <hch@lst.de> 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.
>

Gerald,

Might you still be looking to help dcssblk get out of FS_DAX_LIMITED
jail [1]? I recall Martin saying that 'struct page' overhead was
prohibitive. I don't know if Joao's 'struct page' diet patches could
help alleviate that at all (would require the filesystem to only
allocate blocks in large page sizes).

[1]: https://lore.kernel.org/r/20180523205017.0f2bc83e@thinkpad