Recent macOS versions zero out memory on free, which improves the efficacy of memory compression. Apparently it’s a net performance gain in the average case

A few years back I patched the memory allocator used by the Cloudflare Workers runtime to overwrite all memory with a static byte pattern on free, so that uninitialized allocations contain nothing interesting.

Note that many malloc implementations will do this for you given an appropriate environment, e.g. setting MALLOC_CONF to opt.junk=free will do this on FreeBSD.

> OpenBSD uses 0xdb to fill newly allocated memory and 0xdf to fill memory upon being freed. This helps developers catch "use-before-initialization" (seeing 0xdb) and "use-after-free" (seeing 0xdf) bugs quickly.

Looks like this is the default in OpenBSD.

You know, I never even considered doing that but it makes sense; whatever overhead that's incurred by doing that static byte pattern is still almost certainly minuscule compared to the overhead of something like a garbage collector.

FYI, at least in C/C++, the compiler is free to throw away assignments to any memory pointed to by a pointer if said pointer is about to be passed to free(), so depending on how you did this, no perf impact could have been because your compiler removed the assignment. This will even affect a call to memset()

see here: https://godbolt.org/z/rMa8MbYox