Re: [Linux-nvdimm] [GIT PULL] PMEM driver for v4.1
From: Yigal Korman
Date: Mon Apr 13 2015 - 07:12:04 EST
On Mon, Apr 13, 2015 at 1:45 PM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> * Christoph Hellwig <hch@xxxxxx> 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?
> Linux-nvdimm mailing list
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/