Performance problems with pagedaemon

[Garrett Cooper]

On Tue, Jan 3, 2012 at 12:05 AM, Victor Balada Diaz <victor at bsdes.net> wrote:
> 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.

    They probably should be mentioned in tuning(7).
Thanks,
-Garrett