Re: aim7 scalability issue on 4 socket machine

["Zhang, Yanmin" <yanmin_zhang@linux.intel.com>]

On Thu, 2009-09-17 at 19:59 -0700, Andrew Morton wrote:
> On Fri, 18 Sep 2009 10:02:19 +0800 "Zhang, Yanmin" <yanmin_zhang@linux.intel.com> wrote:
> 
> > > > Did you see Lee's patch?:
> > > > 
> > > >  http://lkml.org/lkml/2009/9/9/290
> > > > 
> > > > Added Lee and Hugh to CC, retained the below patch for them.
> > > 
> > > Thanks a lot for the CC, Peter.
> > > See my reply to that mail for the slightly corrected version.
> > > 
> > > Yes, Yanmin and Lee appear to be fixing exactly the same issue.
> > > I haven't thought through Yanmin's version for correctness, but
> > > it lacks the vm_start check I added to Lee's, and I do prefer
> > > Lee's style - hey, nothing personal!
> > > 
> > > So, Yanmin, please retest with http://lkml.org/lkml/2009/9/13/25
> > > and let us know if that works as well for you - thanks.
> > I tested Lee's patch and it does fix the issue.
> 
> Do we think we should cook up something for -stable?
It's better to have a patch for -stable.

> 
> Either this is a regression or the workload is particularly obscure. 
This issue is not clear on dual socket Nehalem machine (2*4*2 cpu), but
is severe on large machine (4*8*2 cpu).

> 
> aim7 is sufficiently non-obscure to make me wonder what's happened here?
I copy previous content below:

Aim7 consists of lots of subtests. One test is to fork lots of processes and
every process calls sbrk for 1000 times to grow/shrink the heap. All the vma of
the heap of all sub-processes point to the same anon_vma and use the same
anon_vma->lock. When sbrk is called, kernel calls do_brk => vma_merge =>vma_adjust
and lock anon_vma->lock to create spinlock contentions.