Re: Interesting VM feature?

[mouschi@wi.rr.com]

Jamie Lokier wrote:
> You can call madvise(start, length, MADV_DONTNEED),
> or you can mmap() fresh empty pages into the region.

madvise appears to be exactly what I'm looking for.
(almost...)

> I have no idea if either of these methods is
efficient enough to be
> useful.  Also, I don't know whether mmap() would
create multiple VMAs,
> or if it is clever enough to merge adjacent vmas
of anonymous private
> mappings regardles of offset.

Enough possible pitfalls that madvise becomes the
better solution.

> The ideal implementation would give the kernel the
_option_ of
> discarding pages until they are next touched, so
that they are
> discarded when there is memory pressure but
retained if not, avoiding
> the unnecessary zero-fill and cache flush.

Is madvise required to result in zero filled pages
by a standard, or is this just the commonly accepted
behavior?

> -- Jamie

Thanks a bunch,
Ted