First memory profile in a process is empty

[TheJokr]

Foundations lazily initializes its memory profiling infrastructure on the first request to the telemetry server. This happens here:

foundations/foundations/src/telemetry/server.rs

Lines 172 to 180 in 9a6f4cd

	pub(super) fn profiler(settings: Arc<TelemetrySettings>) -> Result<MemoryProfiler> {
	MemoryProfiler::get_or_init_with(&settings.memory_profiler)?.ok_or_else(|| {
	"profiling should be enabled via `_RJEM_MALLOC_CONF=prof:true` env var".into()
	})
	}
	pub(super) async fn heap_profile(settings: Arc<TelemetrySettings>) -> Result<String> {
	profiler(settings)?.heap_profile().await
	}

MemoryProfiler::get_or_init_with initializes the singleton PROFILER with memory_profiler::init_profiler. Inside the latter function, jemalloc's prof.reset control is used to set the configured sampling rate:

foundations/foundations/src/telemetry/memory_profiler.rs

Lines 168 to 169 in 9a6f4cd

	control::write(control::PROF_RESET, settings.sample_interval as u64)
	.map_err(|e| BootstrapError::new(e).context("failed to set sample interval"))?;

The problem is that prof.reset also resets the profiling data collected so far. Therefore, the first requested profile is empty instead of exposing data since the process started. As a user, this is highly unexpected especially because jemalloc was already collecting the data. I suggest that we perform this setup as part of the telemetry::init call early in the program startup.

[TheJokr]

Just noticed that this likely already is fixed by 25fd859 in 4.0.0, just need to upgrade the library.