You still need locking to make this work in a multithreaded environment, or at least atomics. And all malloc implementations used today are more complex than this, especially when allocating large objects, because you can't actually maintain a list for every possible size of allocation. That means they need to do extra work to handle fragmentation.
Plus, the free list has to occasionally be walked to actually free pages back to the OS. If you don't, then memory is never freed by free(), it is only marked for potential reuse.
There are several popular implementations of malloc (and their corresponding free), and they are all quite complex and have different tradeoffs. And, in fact, none of them is any more suitable for high performance or realtime code than a GC is. The golden rule for writing this type of code is to just never call malloc/free in critical sections.
And I will note that probably the most commonly used malloc, the one in GNU's glibc, actually uses Linux locks, not atomics. Which means that you are virtually guaranteed to deadlock if you try to use malloc() after fork() but before exec() in a multi-threaded process.
Plus, the free list has to occasionally be walked to actually free pages back to the OS. If you don't, then memory is never freed by free(), it is only marked for potential reuse.
There are several popular implementations of malloc (and their corresponding free), and they are all quite complex and have different tradeoffs. And, in fact, none of them is any more suitable for high performance or realtime code than a GC is. The golden rule for writing this type of code is to just never call malloc/free in critical sections.
And I will note that probably the most commonly used malloc, the one in GNU's glibc, actually uses Linux locks, not atomics. Which means that you are virtually guaranteed to deadlock if you try to use malloc() after fork() but before exec() in a multi-threaded process.