Re: [RFC] NUMA futex hashing

Eric Dumazet
2006-08-08T12:29:47Z

On Tuesday 08 August 2006 12:36, Andi Kleen wrote:
> > We may have special case for PRIVATE futexes (they dont need to be
> > chained in a global table, but a process private table)
>
> What do you mean with PRIVATE futex?
>
> Even if the futex mapping is only visible by a single MM mmap_sem is still
> needed to protect against other threads doing mmap.

Hum... I would call that a user error.

If a thread is munmap()ing the vma that contains active futexes, result is
undefined. Same as today I think (a thread blocked in a FUTEX_WAIT should
stay blocked)

The point is that private futexes could be managed using virtual addresses,
and no call to find_extend_vma(), hence no mmap_sem contention.

There could be problem if the same futex (32 bits integer) could be mapped at
different virtual addresses in the same process.

Eric