Re: [RFC V2 SLEB 00/14] The Enhanced(hopefully) Slab Allocator

[Nick Piggin <npiggin@suse.de>]

On Thu, May 27, 2010 at 11:57:54AM -0500, Christoph Lameter wrote:
> On Fri, 28 May 2010, Nick Piggin wrote:
> 
> > > > realized that incremental improvements to SLAB would likely be a
> > > > far better idea.
> > >
> > > It looked to me as if there was a major conceptual issue with the linked
> > > lists used for objects that impacted performance
> >
> > With SLQB's linked list? No. Single threaded cache hot performance was
> > the same (+/- a couple of cycles IIRC) as SLUB on your microbenchmark.
> > On Intel's OLTP workload it was as good as SLAB.
> >
> > The linked lists were similar to SLOB/SLUB IIRC.
> 
> Yes that is the problem. So it did not address the cache cold
> regressions in SLUB. SLQB mostly addressed the slow path frequency on
> free.

This is going a bit off topic considering that I'm not pushing SLQB
or any concept from SLQB (just yet at least). As far as I know there
were no cache cold regressions in SLQB.


> The design of SLAB is superior for cache cold objects since SLAB does
> not touch the objects on alloc and free (if one requires similar
> cache cold performance from other slab allocators) thats why I cleaned
> up the per cpu queueing concept in SLAB (easy now with the percpu
> allocator and operations) and came up with SLEB. At the same time this
> also addresses the slowpath issues on free. I am not entirely sure how to
> deal with the NUMAness but I want to focus more on machines with low node
> counts.
> 
> The problem with SLAB was that so far the "incremental improvements" have
> lead to more deteriorations in the maintainability of the code. There are
> multiple people who have tried going this route that you propose.

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