Well that doesn't help in this case. I tested and the mmap_sem contention
is not an issue.
The idea is a good one, and I was half way through implementing similar
myself at one point (some java apps hit this badly).
It is just horribly sad that futexes are supposed to implement a
_scalable_ thread synchronisation mechanism, whilst fundamentally
relying on an mm-wide lock to operate.
I don't like your interface, but then again, the futex interface isn't
exactly pretty anyway.
You should resubmit the patch, and get the glibc guys to use it.
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