swap/io metric incorrectly named

[tomusher]

The swap/io metric is documented as "Total count of swap I/O operations by direction.", and labelled "Swap I/O operations" in the monitoring dashboard.

However, this seems to be a rename of the OpenTelemetry system.paging.operations metric, documented as "The number of paging operations.".

As this is related to all paging operations not just those related to swap, and not necessarily related to I/O, this metric seems to be incorrectly labelled and named which caused us some confusion when we were tracing swap behavior but not seeing any actual swap operations.

[quentinmit]

I think this actually changed. The comments in Ops Agent's code say that there's only one value for type:

ops-agent/apps/hostmetrics.go

Lines 227 to 236 in 30f817f

	otel.RenameMetric(
	"system.paging.operations",
	"swap/io",
	// delete single-valued type dimension, retaining only direction
	otel.AggregateLabels("sum", "direction"),
	otel.RenameLabelValues("direction", map[string]string{
	"page_in": "in",
	"page_out": "out",
	}),
	),

But it looks like system.paging.operations actually reports 4 different time series now:

https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/4ad228de63885a2a623b275b2eeabb84362e6204/receiver/hostmetricsreceiver/internal/scraper/pagingscraper/paging_scraper_others.go#L122-L127

and it looks like the minor streams actually double-count swap page-ins that were already counted in major, AND it looks like it's reporting bytes instead of operations:

https://github.com/shirou/gopsutil/blob/v4.25.7/mem/mem_linux.go#L336-L379

so I think we need to filter by type == "major" and also divide by 4096 to get the right values (yikes!)

[github-actions]

This issue was marked stale due to lack of activity. It will be closed in 14 days.

[ViliusS]

Please correct the name of this metric. I've spent hours investigating why one of our VMs goes into swapiness state because this metric reported extensive swap IO, but after that I realized that GCE VMs do not have swap enabled at all.