[ofa-general] Re: [patch 5/9] Convert anon_vma lock to rw_sem and refcount

Andrea Arcangeli
2008-04-02T22:12:28Z

On Wed, Apr 02, 2008 at 02:56:25PM -0700, Christoph Lameter wrote:
> I am a bit surprised that brk performance is that important. There may be

I think it's not brk but fork that is being slowed down, did you
oprofile? AIM forks a lot... The write side fast path generating the
overscheduling I guess is when the new vmas are created for the child
and queued in the parent anon-vma in O(1), so immediate, even
preempt-rt would be ok with it spinning and not scheduling, it's just
a list_add (much faster than schedule() indeed). Every time there's a
collision when multiple child forks simultaneously and they all try to
queue in the same anon-vma, things will slowdown.