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

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Date:	Fri, 23 Jan 2009 12:13:32 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Nick Piggin <npiggin@...e.de>,
	Linux Memory Management List <linux-mm@...ck.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Lin Ming <ming.m.lin@...el.com>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Christoph Lameter <clameter@...r.sgi.com>
Subject: Re: [patch] SLQB slab allocator

Hi Andi,

On Fri, 2009-01-23 at 10:55 +0100, Andi Kleen wrote:
> > +#if L1_CACHE_BYTES < 64
> > +	if (size > 64 && size <= 96)
> > +		return 1;
> > +#endif
> > +#if L1_CACHE_BYTES < 128
> > +	if (size > 128 && size <= 192)
> > +		return 2;
> > +#endif
> > +	if (size <=	  8) return 3;
> > +	if (size <=	 16) return 4;
> > +	if (size <=	 32) return 5;
> > +	if (size <=	 64) return 6;
> > +	if (size <=	128) return 7;
> > +	if (size <=	256) return 8;
> > +	if (size <=	512) return 9;
> > +	if (size <=       1024) return 10;
> > +	if (size <=   2 * 1024) return 11;
> > +	if (size <=   4 * 1024) return 12;
> > +	if (size <=   8 * 1024) return 13;
> > +	if (size <=  16 * 1024) return 14;
> > +	if (size <=  32 * 1024) return 15;
> > +	if (size <=  64 * 1024) return 16;
> > +	if (size <= 128 * 1024) return 17;
> > +	if (size <= 256 * 1024) return 18;
> > +	if (size <= 512 * 1024) return 19;
> > +	if (size <= 1024 * 1024) return 20;
> > +	if (size <=  2 * 1024 * 1024) return 21;
> 
> Have you looked into other binsizes?  iirc the original slab paper
> mentioned that power of two is usually not the best.

Judging by the limited boot-time testing I've done with kmemtrace, the
bulk of kmalloc() allocations are under 64 bytes or so and actually a
pretty ok fit with the current sizes. The badly fitting objects are
usually very big and of different sizes (so they won't share a cache
easily) so I'm not expecting big gains from non-power of two sizes.

			Pekka

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