mi_new(256) distribute 64M Virtual Memory

[xty438307820]

I try to call mi_new(256) in mimalloc-2.0.6. Then use top to see the VIRT, I found the VIRT increase 64M, why I just need 256B, the mimalloc mmap 64M memory. Can I decrease this value. Incase I want to run many robot process, every process need extra 64M is too large.

int main()
{
mi_new(256);
while(1);
return 0;
}

Thank you!

[daanx]

Mimalloc always reserves memory space up front -- but it's virtual; that is, just some numbers to the OS. Only later it will commit on-demand. I guess you are on 32-bit though -- in such case the virtual reservation is a bit limiting since we only have 4GiB virtual; in that case you could give a smaller arena reservation, like MIMALLOC_ARENA_RESERVE=8MiB ... but not much lower though since segments are 4MiB on 32-bit. Mimalloc may not be the right allocator if you have many processes in a 32-bit environment that all compete for virtual memory (but isn't virtual memory 4GiB per process ? -- in that case there as no problem since arena's are shared between threads)