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    SubjectRe: [PATCH] rmap 18 i_mmap_nonlinear
    On Wed, 28 Apr 2004, William Lee Irwin III wrote:
    >> I believe the flush_dcache_page() implementations touching
    >> ->i_mmap_shared care about this distinction.

    On Thu, Apr 29, 2004 at 07:10:59AM +0100, Hugh Dickins wrote:
    > That's right, arm and parisc do handle them differently: currently
    > arm ignores i_mmap (and I think rmk was wondering a few months ago
    > whether that's actually correct, given that MAP_SHARED mappings
    > which can never become writable go in there - and that surprise is
    > itself a very good reason for combining them), and parisc... ah,
    > what it does in Linus' tree at present is about the same for both,
    > but there are some changes on the way.
    > The differences are not going to be enough to deserve two separate
    > prio_tree_roots in every struct address_space, we can check vm_flags
    > for any differences if necessary.

    It seemed these two actually wanted a precise recovery of virtual
    addresses and the like for flush_dcache_page() like they would have
    had with pte_chains, but never got around to using it.

    On Thu, Apr 29, 2004 at 07:10:59AM +0100, Hugh Dickins wrote:
    > Something else I should have commented on, in that patch comment or
    > the next: although we now have the separate i_mmap_nonlinear list,
    > no attempt to search it for nonlinear pages in flush_dcache_page.
    > It looks like parisc has no sys_remap_file_pages syscall anyway,
    > and arm only flushes current active_mm, so should be okay so long
    > as people don't mix linear and nonlinear maps of same pages (hmm,
    > and don't map same page twice in a nonlinear: more likely) in same
    > mm: anyway, I think any problems there have to be a "Don't do that",
    > searching page tables in flush_dcache_page would be too too painful.

    Maybe it's worth #ifdef'ing out core remap_file_pages() support for
    those arches if all it can do is harm to them wrt. cache coherency
    issues. ARM probably wouldn't mind conserving the code it otherwise
    wouldn't use.

    -- wli
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