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SubjectRe:mmap(MAP_SHARED | MAP_ANON) broke!

Sujal Patel <> wrote:
> Are there any plans for fixing anonymous shared mmap()? I really
> need this too work.

I guess you need this so that the anon mapped pages are not marked
COW upon fork().

It is possible to edit do_mmap() to allow this flag combination (I
haven't tried it though), but be WARNED! Shared anon pages are not
paged out to swap! Only anon pages with a ref of 1 are pagable
(changing this restriction is non-trivial).
There might be another problem, or two, but if you have enough
memory just try changing do_mmap() and see what happens.

When my current contract finishes here (couple of weeks), I'll
hopefully have enough time to code my idea of how the VM subsystem
should be implemented. The "can't page shared anon pages"
restriction is one I'm planning to remove (but don't hold your
breath waiting for it...).



Mark Hemment, UNIX/C Software Engineer (Contractor)

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