Allocation of memory by zalloc

Question

I am going through the perf source in linux kernel source to find out how user space probing is implemented. At many places, I encountered this :

zalloc(sizeof(struct __event_package) * npevs);

I think its located in zlib library (for fedora 18). Can anybody tell me how this zalloc helps in allocating memory? Thanks in advance...

Answer 1

You can refer this link:

The allocation is the same as any other heap allocation. In the kernel space, heap is divided into many freelists, and each freelist has blocks of same sizes connected in a linked list.

For eg:
Freelist1 - 4 bytes/block x 10 blocks
Freelist2 - 8 bytes/block x 10 blocks
Freelist3 - 16 bytes/block x 10 blocks
....
Freelist10 - 1024 bytes/block x 10 blocks

Each free list represents slabs (slab allocator) and make use of buddy system

So, when one does a zalloc, it first decides which size freelist can fulfill this request and then finds a free blocks from it.

In some custom kernel implementations, heap is divided amongst kernel & other services. In that case, *alloc needs to know which heap to access to fulfill the request.