Performance problems with pagedaemon

[Victor Balada Diaz]

On Mon, Jan 02, 2012 at 10:17:11AM -0800, Artem Belevich wrote:
> On Mon, Jan 2, 2012 at 5:41 AM, Victor Balada Diaz <victor at bsdes.net> wrote:
>
> Mysql uses more than 20G of RAM. You may want to tune it down a bit so
> that there is a bit of free RAM around.
> 
> Page daemon is trying to maintain v_free_target + v_cache_min.
> 
> >vm.v_free_target: 161771
> >vm.v_cache_min: 161771
> 
> In your case that would be about 1.2GB. If 'v_free_count +
> v_cache_count' are below that page daemon will periodically wake up
> and will start scanning active/inactive lists trying to find the pages
> it could use. In your case, when most of the memory is in active use,
> page daemon's job will be almost pointless and would just waste CPU
> time.
> 
> On large memory systems default tuning for v_free/cache_min/target is
> probably somewhat conservative. You may try setting them somewhat
> lower via sysctl and see if you can find an equilibrium with mysql
> happy, pagedaemon sleeping and the system up and running. The danger
> of tuning these parameters too low is that is you don't have enough
> memory available for allocation without having to sleep, things will
> start falling apart and will eventually hang or crash your box.

That was the problem. Thanks a lot!

Is there any place or documentation about how to properly tune the VM? None
of the sysctls you mentioned have description or appear to be in any man
page.

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