x2 memory usage + potentially memory leak.

[punksta]

I was debugging out-of-memory errors of production app and found that

1. Hermes used about twice more RAM memory comparing to JSC.
2. it didn't free unused memory.

android performance RAM monitor

tested on:

• react-native 61.5
• debug build type
• production, minified, JS
• android emulator x86, api 29

hermes 0.2.1

JSC r241213

You can clearly see how memory was growing and wasn't getting free

note

I think it's something either related to json parsing or fetch api because the app loads large json objects (10*5mb)

[avp]

This seems related to #164, which discusses a memory leak in WeakMap that was fixed in 0.4.1.

It seems likely that the fix is related to your issue - can you try upgrading Hermes and seeing if that works? Note that Hermes 0.4.1 works with RN 0.62.0.

[punksta]

@avp yep. But I can try upgrading no earlier than next week. JSC solves my current problem

[sinxwal]

@punksta Have you checked Hermes 0.4.1?
In my case the memory usage is still huge.

[punksta]

@sinxwal unfortunately I just switched to JSC and I don't have time for experiments. I will update this issue if I try it.

[sinxwal]

@punksta Thanks, mate. Switching to JSC is so expensive(

[punksta]

@sinxwal you mean things like facebook/react-native#25494 ?
It is painful, but for my current project it isn't as bad as memory leaks. Basically I am just hoping that it will be fixed one day.

[punksta]

I tested the app again.

• React-native 63.2
• production, minified js, release build type, with android studio profiler on
• android v21 emulator

Hermes

JSC

Memory leak seams resolved. Memory usage is also much better.

[tmikov]

@punksta do you have an idea why the Java memory and the stack are so different between the two graphs? Shouldn't they be the same?

[punksta]

@tmikov Indeed stack usage is very different: 20mb (hermes) vs 1.2mb (jsx). But I don't know why, unfortunately

[tmikov]

@punksta AFAICT, it is the opposite: 1.2mb Hermes vs 20mb jsc. That actually makes sense - Hermes doesn't use the native stack, while JSC does. So the Hermes "stack" would count as "native memory". If we add them together we get about 75MB total native memory, approximately the same between both engines. Which is disappointing for us, of course, but not awful.

There are two remaining mysteries:

• Why is the Java memory so different?
• Is your application deeply recursive? 20MB is a lot of stack.

[punksta]

@tmikov you are right. I can't recall any deep recursions in the app.

Let me describe what the app does. It loads about 80mb by chunks and writes it into sqlite.

So data flow is the following:

okhttp -> react-native-fetch-blob -> javascript engine -> react-native-sqlite-2 -> sqlite

I assume that gc could not release memory allocated for java objects in one of these components.
Stack memory was already taken the loading started. So it's something else.

I will try to explore memory dump.