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SubjectRe: Locking comment on shrink_caches()
From: "Andrew Morton" <>
> > John Hawkes from SGI had published some AIM7 numbers that showed
> > pagecache_lock to be a bottleneck above 4 processors. At 32
> > half the CPU cycles were spent on waiting for pagecache_lock. The
> > thread is at -
> >
> >
> >
> 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

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