Re: 2.5.39 kmem_cache bug

[Manfred Spraul <manfred@colorfullife.com>]

What's the optimal number of free objects in the partial/free lists of 
an active cache?

I'd say a few times the batchcount, otherwise a cpu won't be able to 
perform a complete refill. [during refill, at most one grow happens - 
I've assumed that swallowing 30 pages with GFP_ATOMIC in an interrupt 
handler is not nice from the system perspective]

What about this logic:
- if there were no recent allocations performed by a cpu, then return 
cc->limit/5 objects from the cpu array to the node lists.

- If a slab becomes a free slab, and there are more than 
3*cc->batchcount*NR_CPUS/NR_NODES objects in the partial or free lists, 
then return the slab immediately to the gfp.

- If noone accessed the free list recently, then a few slabs are 
returned to gfp. [<worst case number of free slabs that can exist>/5]

The constants could be updated by vm pressure callbacks.

--
	Manfred

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