linux-kernel - Re: [patch] SLQB slab allocator

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Message-ID: <Pine.LNX.4.64.0901141158090.26507@quilx.com>
Date:	Wed, 14 Jan 2009 12:01:32 -0600 (CST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Nick Piggin <npiggin@...e.de>
cc:	Pekka Enberg <penberg@...helsinki.fi>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Lin Ming <ming.m.lin@...el.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [patch] SLQB slab allocator

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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