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    SubjectRe: [PATCH v2 00/10] evacuate struct page from the block layer, introduce __pfn_t
    On 05/08/2015 09:14 PM, Linus Torvalds wrote:
    > On Fri, May 8, 2015 at 9:59 AM, Rik van Riel <riel@redhat.com> wrote:
    >>
    >> However, for persistent memory, all of the files will be "in memory".
    >
    > Yes. However, I doubt you will find a very sane rw filesystem that
    > then also makes them contiguous and aligns them at 2MB boundaries.
    >
    > Anything is possible, I guess, but things like that are *hard*. The
    > fragmentation issues etc cause it to a really challenging thing.

    The TLB performance bonus of accessing the large files with
    large pages may make it worthwhile to solve that hard problem.

    > And if they aren't aligned big contiguous allocations, then they
    > aren't relevant from any largepage cases. You'll still have to map
    > them 4k at a time etc.

    Absolutely, but we only need the 4k struct pages when the
    files are mapped. I suspect a lot of the files will just
    sit around idle, without being used.

    I am not convinced that the idea I wrote down earlier in
    this thread is worthwhile now, but it may turn out to be
    at some point in the future. It all depends on how much
    data people store on DAX filesystems, and how many files
    they have open at once.

    --
    All rights reversed


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