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    SubjectRe: No more bits in vm_area_struct's vm_flags.
    On Mon, 28 Sep 2009 11:36:24 +0800
    Wu Fengguang <fengguang.wu@intel.com> wrote:

    > On Mon, Sep 28, 2009 at 11:04:50AM +0800, KAMEZAWA Hiroyuki wrote:

    > > But, yes it implies to add a new argument to several functions in mmap.c
    > > and maybe a patch will be ugly.
    > >
    > > How about addding this check ?
    > >
    > > is_mergeable_vma(...)
    > > ....
    > > if (vma->vm_hints)
    > > return 0;
    > >
    > > And not calling vma_merge() at madvice(ACCESS_PATTERN_HINT).
    > >
    > > I wonder there are little chances when madice(ACCESS_PATTERN_HINT) is
    > > given against mapped-file-vma...
    >
    > Me wonder too. The access hints should be rarely used.
    > A simple solution is reasonable for them.
    >
    > But what if more flags going into vm_hints in future?
    >

    yes, that's concern...

    But I wonder there are several flags which implies that the vma is not for
    merge. as....

    #define VM_GROWSDOWN 0x00000100 /* general info on the segment */
    #define VM_GROWSUP 0x00000200

    or some PFN_MAP flags...
    (At least, we can have 4 flags of not-for-merge in vm_hints ;)

    Then, Nigel, you have 2 choices I think.

    (1) don't merge if vm_hints is set or
    (2) pass vm_hints to all __merge() functions.

    One of above will be accesptable for stakeholders...
    I personally like (1) but just trying (2) may be accepted.

    What I dislike is making vm_flags to be long long ;)

    Thanks,
    -Kame



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