[sldev] Optimization via _set_sbh_threshold

Dirk Moerenhout blakar at gmail.com
Wed Jun 13 05:05:31 PDT 2007


Nick,

indeed. Although I doubt they disabled SBH to promote LFH. I think
they figured SBH would no longer play a role in todays workloads. I'm
hence not so sure that SBH holds up when facing heavy load. SBH's
locking code and ability to handle huge heaps (containing megabytes of
small items) may be bad as it was written in a different age. They
started working on LFH when 64MB was considered a lot of RAM. And as
they turned off SBH they must've figured it would be no longer
applicable for software with big memory footprints.

I'm for example not sure how SBH is doing alignment. For LFH it's
clear that minimum size is 8 bytes and it's known to be ready for 64
bits environments. I'm pretty sure it'll align well to avoid
performance hits.

Dirk aka Blakar Ogre

On 6/13/07, Nicholaz Beresford <nicholaz at blueflash.cc> wrote:
>
> Hmm.... am I getting this right?
>
> LFH is an improvement over SBH but needs to be activated and
> in order to promote it the turned off SBH by default?
>
> I'll test more in direction of activating LFH then ...
>
>
> Nick
>
>
>
>
>


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