Re: [RFC] Simple Slab: A slab allocator with minimal meta information

[Manfred Spraul <manfred@colorfullife.com>]

Christoph Lameter wrote:

>I still do not get the role of the shared cache though.
>
The shared cache is just for efficient object transfers:
Think about two nics, both cpu bound, one does rx, the other does tx.
Result: a few 100k kmalloc, kmem_cache_alloc(skb_head_cache) calls each 
second on cpu1.
the same number of kfree, kmem_cache_free(skb_head_cache) calls each 
second on cpu 2.

What is needed is an efficient algorithm for transfering all objects 
from cpu 2 to cpu 1.
Initially, the slab allocator just had the cpu cache. Thus an object 
transfer was a free_block call: add the freed object to the bufctl 
linked list. Move the slab to the tail of the partial list. Probably the 
list_del()/list_add() calls caused cache line trashing, but I don't 
remember the details. IIRC Robert Olsson did the test. Pentium III Xeon 
system?
Anyway: The solution was the shared array. It allows to move objects 
around with a simple memmove of the pointers, without the 
list_del()/list_add() calls.

--
    Manfred