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    SubjectRe: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear)
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    On Tuesday 13 March 2007 02:19, Nick Piggin wrote:
    > On Tue, Mar 13, 2007 at 12:01:13AM +0100, Blaisorblade wrote:
    > > On Wednesday 07 March 2007 11:02, Nick Piggin wrote:
    > > > > Yeah, tmpfs/shm segs are what I was thinking about. If UML can live
    > > > > with that as well, then I think it might be a good option.
    > > >
    > > > Oh, hmm.... if you can truncate these things then you still need to
    > > > force unmap so you still need i_mmap_nonlinear.
    > >
    > > Well, we don't need truncate(), but MADV_REMOVE for memory hotunplug,
    > > which is way similar I guess.
    > >
    > > About the restriction to tmpfs, I have just discovered
    > > '[PATCH] mm: tracking shared dirty pages' (commit
    > > d08b3851da41d0ee60851f2c75b118e1f7a5fc89), which already partially
    > > conflicts with remap_file_pages for file-based mmaps (and that's fully
    > > fine, for now).
    > >
    > > Even if UML does not need it, till now if there is a VMA protection and a
    > > page hasn't been remapped with remap_file_pages, the VMA protection is
    > > used (just because it makes sense).
    > >
    > > However, it is only used when the PTE is first created - we can never
    > > change protections on a VMA - so it vma_wants_writenotify() is true (on
    > > all file-based and on no shmfs based mapping, right?), and we
    > > write-protect the VMA, it will always be write-protected.
    >
    > Yes, I believe that is the case, however I wonder if that is going to be
    > a problem for you to distinguish between write faults for clean writable
    > ptes, and write faults for readonly ptes?
    I wouldn't be able to distinguish them, but am I going to get write faults for
    clean ptes when vma_wants_writenotify() is false (as seems to be for tmpfs)?
    I guess not.

    For tmpfs pages, clean writable PTEs are mapped as writable so they won't give
    any problem, since vma_wants_writenotify() is false for tmpfs. Correct?

    > > Also, I'm curious. Since my patches are already changing
    > > remap_file_pages() code, should they be absolutely merged after yours?
    >
    > Is there a big clash? I don't think I did a great deal to fremap.c (mainly
    > just removing stuff)...
    Hopefully, we just both modify sys_remap_file_pages(), I'll see soon.
    --
    Inform me of my mistakes, so I can add them to my list!
    Paolo Giarrusso, aka Blaisorblade
    http://www.user-mode-linux.org/~blaisorblade
    Chiacchiera con i tuoi amici in tempo reale!
    http://it.yahoo.com/mail_it/foot/*http://it.messenger.yahoo.com

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