* Michel Lespinasse <wal...@google.com> wrote:
> On Sun, Nov 10, 2013 at 8:12 PM, Davidlohr Bueso <davidl...@hp.com> wrote:
> > 2) Oracle Data mining (4K pages)
> > +------------------------+----------+------------------+---------+
> > | mmap_cache type | hit-rate | cycles (billion) | stddev |
> > +------------------------+----------+------------------+---------+
> > | no mmap_cache | - | 63.35 | 0.20207 |
> > | current mmap_cache | 65.66% | 19.55 | 0.35019 |
> > | mmap_cache+largest VMA | 71.53% | 15.84 | 0.26764 |
> > | 4 element hash table | 70.75% | 15.90 | 0.25586 |
> > | per-thread mmap_cache | 86.42% | 11.57 | 0.29462 |
> > +------------------------+----------+------------------+---------+
> >
> > This workload sure makes the point of how much we can benefit of
> > caching the vma, otherwise find_vma() can cost more than 220% extra
> > cycles. We clearly win here by having a per-thread cache instead of
> > per address space. I also tried the same workload with 2Mb hugepages
> > and the results are much more closer to the kernel build, but with the
> > per-thread vma still winning over the rest of the alternatives.
> >
> > All in all I think that we should probably have a per-thread vma
> > cache. Please let me know if there is some other workload you'd like
> > me to try out. If folks agree then I can cleanup the patch and send it
> > out.
>
> Per thread cache sounds interesting - with per-mm caches there is a real
> risk that some modern threaded apps pay the cost of cache updates
> without seeing much of the benefit. However, how do you cheaply handle
> invalidations for the per thread cache ?
The cheapest way to handle that would be to have a generation counter for
the mm and to couple cache validity to a specific value of that.
'Invalidation' is then the free side effect of bumping the generation
counter when a vma is removed/moved.
Thanks,
Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
