MemoryGauge app: log memory in use for workers in SHM and RRD

[eugeneia]

• Adds a SHM type “gauge“ for double precision floating point values
• Adds an app that periodically writes collectgarbage('count') (kbytes in use) to a SHM gauge (and configure it for lwaftr workers)
• Extend ptree manager to aggregate gauge RRDs

The result is that lwaftr instances have RRDs like apps/memory_monitor/kbytes_in_use.rrd which you can plot with rrdtool graph to get graphs like the following:

[wingo]

Looks great, thanks. Two questions: one, do you think this makes sense as an app? To me it's more like a timer, like the ingress drop monitor, or the ptree manager stuff. WDYT? Would be a small change but if you feel it's better as an app I'm happy to hear that argument. Second, do you have a use example? :-) Really cool hack, looks quite useful!

[eugeneia]

Looks great, thanks. Two questions: one, do you think this makes sense as an app? To me it's more like a timer, like the ingress drop monitor, or the ptree manager stuff. WDYT? Would be a small change but if you feel it's better as an app I'm happy to hear that argument. Second, do you have a use example? :-) Really cool hack, looks quite useful!

Doesn’t need to be an app, and I agree its somewhat counter intuitive. The reason it is an app are for convenience:

• convenient reuse of the app SHM frame mechanic
• can be easily configured per process using the ptree infrastructure

[wingo]

Thanks!