[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

--- Comment #8 from David Chisnall <theraven at FreeBSD.org> ---
(In reply to Bill Sorenson from comment #7)

As I said above, there is no mechanism for doing this with shared memory
segments - we cannot zero pages in the middle of a shared-memory segment
without using memset / bzero and this does not allow the kernel to decommit the
physical pages.  I haven't tested whether MAV_FREE allows the kernel to lazily
replace the pages with zeroed pages, but for our uses we need to guarantee
zeroing.

On Linux you can do this with some forms of shared memory using fallocate to
punch a hole in the underlying object, though apparently it isn't very
reliable.

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