lkml.org 
[lkml]   [2015]   [Apr]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    SubjectRe: [Linux-nvdimm] [GIT PULL] PMEM driver for v4.1
    From
    On Mon, Apr 13, 2015 at 1:45 PM, Ingo Molnar <mingo@kernel.org> wrote:
    >
    > * Christoph Hellwig <hch@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-nvdimm@lists.01.org
    > https://lists.01.org/mailman/listinfo/linux-nvdimm


    \
     
     \ /
      Last update: 2015-04-13 13:21    [W:2.297 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site