Re: [PATCH] lazy freeing of memory through MADV_FREE

[Nick Piggin]

Rik van Riel wrote:

> I've added a 5th column, with just your mmap_sem patch and
> without my madv_free patch.  It is run with the glibc patch,
> which should make it fall back to MADV_DONTNEED after the
> first MADV_FREE call fails.

Thanks! (I edited slightly so it doesn't wrap)


>   vanilla   new glibc   madv_free    mmap_sem        both
> threads
>
> 1     610         609         596         534         545
> 2    1032        1136        1196        1180        1200
> 4    1070        1128        2014        2027        2024
> 8    1000        1088        1665        2089        2087
> 16    779        1073        1310        2012        1999
>
>
> Not doing the mprotect calls is the big one I guess, especially
> the fact that we don't need to take the mmap_sem for writing.

Yes.


> With both our patches, single and two thread performance with
> MySQL sysbench is somewhat better than with just your patch,
> 4 and 8 thread performance are basically the same and just
> your patch gives a slight benefit with 16 threads.
>
> I guess I should benchmark up to 64 or 128 threads tomorrow,
> to see if this is just luck or if the cache benefit of doing
> the page faults and reusing hot pages is faster than not
> having page faults at all.
>
> I should run some benchmarks on other systems, too.  Some of
> these results could be an artifact of my quad core CPU.  The
> results could be very different on other systems...

I'm getting the 16 core box out of retirement as we speak :)

--
SUSE Labs, Novell Inc.
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