Re: [PATCH] Reduce vm_stat cacheline contention in__vm_enough_memory

[Andrew Morton]

On Thu, 13 Oct 2011 10:54:30 -0500 (CDT)
Christoph Lameter <cl@xxxxxxxxxx> wrote:

> On Thu, 13 Oct 2011, Dimitri Sivanich wrote:
> 
> > > increase the allowed delta per zone if frequent updates occur via the
> > > overflow checks in vmstat.c. See calculate_*_threshold there.
> >
> > I tried changing the threshold in both directions, with slower throughput in
> > both cases.
> 
> If that is the case check for the vm_stat cacheline being shared with
> another hot kernel variable variable. Maybe that causes cacheline
> eviction.

yup.  `nm -n vmlinux'.

> If there are no updates occurring for a while (due to increased deltas
> and/or vmstat updates) then the vm_stat cacheline should be able to stay
> in shared mode in multiple processors and the performance should increase.
> 

We could cacheline align vm_stat[].  But the thing is pretty small - we
couild put each entry in its own cacheline.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/