[Bug 230160] linuxulator doesn't implement madvise(MADV_DONTNEED) and any MADV_ flags with values >= 8 correctly

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=230160

David Chisnall <theraven at FreeBSD.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|linuxulator doesn't         |linuxulator doesn't
                   |implement                   |implement
                   |madvise(MADV_DONTNEED)      |madvise(MADV_DONTNEED) and
                   |correctly                   |any MADV_ flags with values
                   |                            |>= 8 correctly

--- Comment #3 from David Chisnall <theraven at FreeBSD.org> ---
(In reply to Mark Johnston from comment #2)

Sorry, wanting MADV_ZERO is an unrelated issue: we have some code that would
get a very nice perf improvement if we had it.

In our own code, we implement a FreeBSD equivalent of Linux's MADV_DONTNEED by
doing an mmap with MAP_FIXED over the address range.  This works fine for
anonymous memory mappings (which is all that Linux supports), but it means that
we have to fall back to bzero for shared memory (which means that, among other
things, we get a unique physical page for each virtual page, even though
there's a good chance that the pages are going to stay zero for a while).

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