> At the same time though, when I used Chrome's built-in memory profiling I see a bunch of deopt-related strings, so maybe I'm way off base
In my experience, these add up real quick and are often indicators of a larger "instability" issue that remains well after the "deopt churn" appears to settle, but continues manifests in the form of some heavy GC.
Note: many internal structures related to the JIT (IC/hidden classes/code gen etc) can themselves cause sufficient GC pressure, as can the code you described as "de-opted permanently".
In my experience, these add up real quick and are often indicators of a larger "instability" issue that remains well after the "deopt churn" appears to settle, but continues manifests in the form of some heavy GC.
Note: many internal structures related to the JIT (IC/hidden classes/code gen etc) can themselves cause sufficient GC pressure, as can the code you described as "de-opted permanently".
Interestingly it is also possible for the above mentioned GC pressure to itself cause some fun (even more GC pressure): https://bugs.chromium.org/p/v8/issues/detail?id=5456
This may not be the root of your issue, but I would be careful to rule it out entirely to quickly.
Anyways, best of luck!