Re: [RFC] Reimplementation of linux dynamic percpu memory allocator

[Ravikiran G Thirumalai <kiran@in.ibm.com>]

On Mon, Dec 20, 2004 at 07:24:07PM +0100, Manfred Spraul wrote:
> >
> No, not fast path. But it can happen a few thousand times. The slab 
> implementation failed due to heavy internal fragmentation. If your code 
> runs fine with a few thousand users, then there shouldn't be a problem.

If there is a stress test I can use, I can try running it.

> >>>     
> >..
> For non-NUMA systems, I would use get_free_pages() to allocate a 
> multi-page area instead of map_vm_area(). Typically, get_free_pages() is 
> backed by large pte memory and map_vm_area() by normal virtual memory.

Hmm...the arithmetic becomes tricky then.  Right now I allocate
NR_CPUS * PCU_BLOCKSIZE + BLOCK_MANAGEMENT_SIZE amount of KVA for a block,
allocate pages for cpu_possible cpus and map corresponding va space
with allocated pages using map_vm_area.  We may fragment if
NR_CPUS * PCPU_BLOCKSIZE doesn't fit into a proper page order,
also we'd be wasting pages for !cpu_possible(cpus) of NR_CPUS

Thanks,
Kiran