On Thu, 1 Nov 2007, Nick Piggin wrote:
>
> Untested patch follows
Ok, this looks ok.
Except I would remove the VM_MAYSHARE bit from the test.
That whole bit should go, in fact.
We used to make it something different: iirc, a read-only SHARED mapping
was downgraded to a non-shared mapping, because we wanted to avoid some of
the costs we used to have with the VM implementation (actually, I think it
was various filesystems that don't like shared mappings because they don't
have a per-page writeback). But we left the VM_MAYSHARE bit on, to get
/proc/<pid>/mmap things right.
Or something like that. I forget the details. But I *think* we don't
actually need this any more.
But basically, the "right" way to test for shared mappings is historically
to just test the VM_MAYSHARE bit - but not *both* bits. Because VM_SHARE
may have been artificially cleared.
Somebody should double-check my memory.
Linus
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