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

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Message-ID: <Pine.LNX.4.64.0812150758020.16821@quilx.com>
Date:	Mon, 15 Dec 2008 08:02:47 -0600 (CST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Nick Piggin <npiggin@...e.de>
cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	bcrl@...ck.org, list-linux-mm@...ck.org
Subject: Re: [rfc][patch] SLQB slab allocator

On Mon, 15 Dec 2008, Nick Piggin wrote:

> > Does this mean that SLQB is less efficient than SLUB for off node
> > allocations? SLUB can do off node allocations from the per cpu objects. It
> > does not need to make the distinction for allocation.
>
> I haven't measured them, but that could be the case. However I haven't
> found a workload that does a lot of off-node allocations (short lived
> allocations are better on-node, and long lived ones are not going to
> be so numerous).

A memoryless node is a case where all allocations will be like that.

> That's more complexity, though. Given that objects are often hot when
> they are freed, and need to be touched after they are allocated anyway,
> the simple queue seems to be reasonable.

Yup.

> This case does improve the database score by around 1.5-2%, yes. I
> don't know what you mean exactly, though. What case, and what do you
> mean by bad cache unfriendly programming? I would be very interested
> in improving that benchmark of course, but I don't know what you
> suggest by keeping cachelines hot in the right way?

What I was told about the database test is that it collects lists of
objects from various processors that are then freed on a different
processor. This means all objects are cache cold.
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