[dilippkumar]

> which is usually much less performant than GC from various reasons.

Can you elaborate?

I've seen a couple of malloc implementations, and in all of them, free() is a cheap operation. It usually involves setting a bit somewhere and potentially merging with an adjacent free block if available/appropriate.

malloc() is the expensive call, but I don't see how a GC system can get around the same costs for similar reasons.

What am I missing?

[mrkline]

- Like others have said, both malloc()/free() touch a lot of global state, so you either have contention between threads, or do as jemalloc does and keep thread-local pools that you occasionally reconcile.

- A moving (and ideally, generational) GC means that you can recompact the heap, making malloc() little more than a pointer bump.

- This also suggests subsequent allocations will have good locality, helping cache performance.

Manual memory management isn't magically pause-free, you just get to express some opinion about where you take the pauses. And I'll contend that (A) most programmers aren't especially good at choosing when that should be, and (B) lots (most?) software cares about overall throughput, so long as max latency stays under some sane bound.

[riku_iki]

> Can you elaborate?

I've seen some benchmarks, but can't find them now, so maybe I am wrong about this.

> free() is a cheap operation. It usually involves setting a bit somewhere and potentially merging with an adjacent free block if available/appropriate.

there is some tree like structure somewhere, which then would allow to locate this block for "malloc()", this structure has to be modified in parallel by many concurrent threads, which likely will need some locks, meaning program operates outside of CPU cache.

In JVM for example, GC is integrated into thread models, so they can have heap per thread, and also "free()" happens asynchronously, so doesn't block calling code. Additionally, malloc approaches usually suffer from memory fragmentation, while JVM GC is doing compactions all the time in background, tracks memory blocks generations, and many other optimizations.

[tcfhgj]

Sub (ignore pls)