On Mon, Apr 13, 2015 at 1:45 PM, Ingo Molnar <mi...@kernel.org> wrote: > > * 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. )
mlock() and MAP_POPULATE don't work with DAX files as well. > > 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 > _______________________________________________ > Linux-nvdimm mailing list > linux-nvd...@lists.01.org > https://lists.01.org/mailman/listinfo/linux-nvdimm -- 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/
