Re: anon_vma RFC2

From: William Lee Irwin III
Date: Fri Mar 12 2004 - 07:48:05 EST

On Fri, Mar 12, 2004 at 01:21:27PM +0100, Andrea Arcangeli wrote:
> you missed the fact mremap doesn't work, that's the fundamental reason
> for the vma tracking, so you can use vm_pgoff.
> if you take Hugh's anonmm, mremap will be attaching a persistent dynamic
> overhead to the vma it touches. Currently it does in form of pte_chains,
> that can be converted to other means of overhead, but I simply don't
> like it.
> I like all vmas to be symmetric to each other, without special hacks to
> handle mremap right.
> We have the vm_pgoff to handle mremap and I simply use that.

Absolute guarantees are nice but this characterization is too extreme.
The case where mremap() creates rmap_chains is so rare I never ever saw
it happen in 6 months of regular practical use and testing. Their
creation could be triggered only by remap_file_pages().

-- wli
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