Re: [patch] SLQB slab allocator

[Christoph Lameter]

On Wed, 14 Jan 2009, Nick Piggin wrote:

> Right, but that regression isn't my only problem with SLUB. I think
> higher order allocations could be much more damaging for more a wider
> class of users. It is less common to see higher order allocation failure
> reports in places other than lkml, where people tend to have systems
> stay up longer and/or do a wider range of things with them.

The higher orders can fail and will then result in the allocator doing
order 0 allocs. It is not a failure condition. Higher orders are an
advantage because they localize variables of the same type and therefore
reduce TLB pressure.

> The idea of removing queues doesn't seem so good to me. Queues are good.
> You amortize or avoid all sorts of things with queues. We have them
> everywhere in the kernel ;)

Queues require maintenance which introduces variability because queue
cleaning has to be done periodically and the queues grow in number if NUMA
scenarios have to be handled effectively. This is a big problem for low
latency applications (like in HPC). Spending far too much time optimizing
queue cleaning in SLAB lead to the SLUB idea.
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