* Christoph Hellwig <h...@lst.de> wrote: > On Mon, Apr 13, 2015 at 11:33:09AM +0200, Ingo Molnar wrote: > > Limitations: this is a regular block device, and since the pmem areas > > are not struct page backed, they are invisible to the rest of the > > system (other than the block IO device), so direct IO to/from pmem > > areas, direct mmap() or XIP is not possible yet. The page cache will > > also shadow and double buffer pmem contents, etc. > > Unless you use the DAX support in ext2/4 and soon XFS, in which case > we avoid that double buffering when doing read/write and mmap
Indeed, I missed that DAX support just went upstream in v4.0 - nice! DAX may have some other limitations though that comes from not having struct page * backing and using VM_MIXEDMAP, the following APIs might not work on DAX files: - splice - zero copy O_DIRECT into DAX areas. - futexes - ( AFAICS hugetlbs won't work on DAX mmap()s yet - although with the current nocache mapping that's probable the least of the performance issues for now. ) Btw., what's the future design plan here? Enable struct page backing, or provide special codepaths for all DAX uses like the special pte based approach for mmap()s? Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/