On 8/20/21 6:42 PM, Dan Williams wrote: > On Fri, Aug 20, 2021 at 8:41 AM Dan Williams <dan.j.williams@xxxxxxxxx> wrote: >> >> [ add Gerald and Joao ] >> >> On Thu, Aug 19, 2021 at 10:44 PM 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. >>> >> >> 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). /me nods Either that or dynamically remapping the deduplicated tail page vmemmap areas when we punch holes in what was represented as a compound page (or when we collapse pages back together). Not sure how crazy the latter is. >> >> [1]: https://lore.kernel.org/r/20180523205017.0f2bc83e@thinkpad >
