Re: Locking comment on shrink_caches()

[John Hawkes]

From: "Andrew Morton" <[e-mail]>
> > John Hawkes from SGI had published some AIM7 numbers that showed
> > pagecache_lock to be a bottleneck above 4 processors. At 32
processors,
> > half the CPU cycles were spent on waiting for pagecache_lock. The
> > thread is at -
> >
> > http://marc.theaimsgroup.com/?l=lse-tech&m=98459051027582&w=2
> >
>
> That's NUMA hardware.   The per-hashqueue locking change made
> a big improvement on that hardware.  But when it was used on
> Intel hardware it made no measurable difference at all.

More specifically, that was on SGI Origin2000 32p mips64 ccNUMA
hardware.  The pagecache_lock bottleneck is substantially less on SGI
Itanium ccNUMA hardware running those AIM7 workloads.  I'm seeing
moderately significant contention on the Big Kernel Lock, mostly from
sys_lseek() and ext2_get_block().

John Hawkes
[e-mail]