How can mimalloc manage a piece of allocated memory?

[CS0522]

How can mimalloc manage a piece of allocated memory?

[daanx]

Yes, mimalloc has mi_manage_os_memory for this purpose:

bool mi_manage_os_memory(void* start, size_t size, bool is_committed, bool is_large, bool is_zero, int numa_node);

This will add the memory area to the mimalloc arena's from which it will allocate its memory (use numa_node=-1 for no NUMA preference). There is no need for a specific heap, just mi_malloc will work. It is best if the area is as large as possible such that mimalloc can manage it most effectively with regard to fragmentation.

Hope this helps,
Daan

ps. There is also an extended api, mi_manage_os_memory_ex
to reserve "exclusive" memory that can only be used with heaps attached to such memory (mi_heap_new_in_arena) but I don't think that is what you are asking? (this is used for example to implement compressed pointers in the Koka language using a 4GiB exclusive area for language allocations)

[CS0522]

Thanks very much for your help! It really does me a favor. mimalloc is very useful, and my project cannot be done without it.

[gulmezmerve]

@daanx I am a bit confused about how the mimalloc uses the process memory initially. As far as I know, when the process starts, it already reserves some memory area for the heap, and libc uses sbrk to extend.

But I can track mimalloc down, I understand that it does mmap do manage the memory, right?

Also, what is the alignment-requirement for the mimalloc?

[daanx]

Ah, mimalloc generally does not use sbrk (as that doesn't allow returning (purging) memory back to the OS), and we try to use mmap on most unix systems. See https://github.com/microsoft/mimalloc/blob/dev/src/prim/unix/prim.c for the primitives. Mimalloc allocates it's OS memory with 4MiB alignment (on 64-bit systems).

[gulmezmerve]

thank you for the clarification!