Re: [RFC PATCH v2 0/4] Eliminate zone->lock contention for will-it-scale/page_fault1 and parallel free

[Daniel Jordan]

On 03/21/2018 09:30 PM, Aaron Lu wrote:
> On Wed, Mar 21, 2018 at 01:44:25PM -0400, Daniel Jordan wrote:
> > On 03/20/2018 04:54 AM, Aaron Lu wrote:
> > ...snip...
> > > reduced zone->lock contention on free path from 35% to 1.1%. Also, it
> > > shows good result on parallel free(*) workload by reducing zone->lock
> > > contention from 90% to almost zero(lru lock increased from almost 0 to
> > > 90% though).
> >
> > Hi Aaron, I'm looking through your series now.  Just wanted to mention that I'm seeing the same interaction between zone->lock and lru_lock in my own testing.  IOW, it's not enough to fix just one or the other: both need attention to get good performance on a big system, at least in this microbenchmark we've both been using.
>
> Agree.
>
> > There's anti-scaling at high core counts where overall system page faults per second actually decrease with more CPUs added to the test.  This happens when either zone->lock or lru_lock contention are completely removed, but the anti-scaling goes away when both locks are fixed.
> >
> > Anyway, I'll post some actual data on this stuff soon.
>
> Looking forward to that, thanks.
>
> In the meantime, I'll also try your lru_lock optimization work on top of
> this patchset to see if the lock contention shifts back to zone->lock.

The lru_lock series I posted is pretty outdated by now, and I've got a 
totally new approach I plan to post soon, so it might make sense to wait 
for that.