On 8/13/2015 1:14 PM, Jeff Moyer wrote: > Linda Knippers <linda.knippers@xxxxxx> writes: > >>> I'd be fine with changing the persistent memory block device to only >>> support 4k logical, 4k physical block size. That probably makes the >>> most sense. >> >> If that's what we want, the current patch doesn't do that. >> https://lists.01.org/pipermail/linux-nvdimm/2015-July/001555.html >> >> It causes the physical block size to be PAGE_SIZE but the >> logical block size is still 512. However, the minimum_io_size >> is now 4096 (same as physical block size, I assume). The >> optimal_io_size is still 0. What does that mean? > > physical block size - device's internal block size > logical block size - addressable unit Right, but it's still reported as 512 and that doesn't work. > optimal io size - device's preferred unit for streaming So 0 is ok. > minimum io size - device’s preferred minimum unit for random I/O > > See Martin Petersen's "Linux & Advanced Storage Interfaces" document for > more information. > >> Whatever we go with, we should do something because 4.2rc6 is still >> broken, unable to create a xfs file system on a pmem device, ever >> since the change to use DAX on block devices with O_DIRECT. > > We can change the block device to export logical/physical block sizes of > PAGE_SIZE. However, when persistent memory support comes to platforms > that support page sizes > 32k, xfs will again run into problems (Dave > Chinner mentioned that xfs can't deal with logical block sizes >32k.) > Arguably, you can use pmem and dax on such platforms using RAM today for > testing. Do we care about breaking that? I would think so. AARCH64 uses 64k pages today. I think Documentation/filesystems/dax.txt could use a little update too. It has a section "Implementation Tips for Block Driver Writers" that makes it sound easy but now I wonder if it even works with the example ram drivers. Should we be able to read any 512 byte "sector"? -- ljk > > Cheers, > Jeff > -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
