Ulrich Drepper wrote:
Nick Piggin wrote:
What I found is that, on this system, MADV_FREE performance improvement
was in the noise when you look at it on top of the MADV_DONTNEED glibc
and down_read(mmap_sem) patch in sysbench.
I don't want to judge the numbers since I cannot but I want to make an
observations: even if in the SMP case MADV_FREE turns out to not be a
bigger boost then there is still the UP case to keep in mind where Rik
measured a significant speed-up. As long as the SMP case isn't hurt
this is reaosn enough to use the patch. With more and more cores on one
processor SMP systems are pushed evermore to the high-end side. You'll
find many installations which today use SMP will be happy enough with
many-core UP machines.
OK, sure. I think we need more numbers though.
And even if this was a patch with _no_ possibility for regressions and it
was a completely trivial one that improves performance in some cases...
one big problem is that it uses another page flag.
I literally have about 4 or 5 new page flags I'd like to add today :) I
can't of course, because we have very few spare ones left.
From the MySQL numbers on this system, it seems like performance is in the
noise, and MADV_DONTNEED makes the _vast_ majority of the improvement.
This is also the case with Rik's benchmarks, and while he did see some
improvement, I found the runs to be quite variable, so it would be ideal
to get a larger sample.
And the fact that the poor behaviour of the old style malloc/free went
unnoticed for so long indicates that it won't be the end of the world if
we didn't merge MADV_FREE right now.
--
SUSE Labs, Novell Inc.
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