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Subject: Re: [RFC/PATCH] powerpc: Dynamically allocate pacas
From: Michael Ellerman <michael@ellerman.id.au>
To: Michael Neuling <mikey@neuling.org>
In-Reply-To: <31712.1264130388@neuling.org>
References: <39fb8f1aeab9940b86c940b9a5f8e6bd41ec316c.1263368253.git.michael@ellerman.id.au>
	<31712.1264130388@neuling.org>
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Date: Wed, 27 Jan 2010 14:06:52 +1100
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On Fri, 2010-01-22 at 16:19 +1300, Michael Neuling wrote:
>=20
> In message <39fb8f1aeab9940b86c940b9a5f8e6bd41ec316c.1263368253.git.micha=
el@ell
> erman.id.au> you wrote:
> > On 64-bit kernels we currently have a 512 byte struct paca_struct for
> > each cpu (usually just called "the paca"). Currently they are staticall=
y
> > allocated, which means a kernel built for a large number of cpus will
> > waste a lot of space if it's booted on a machine with few cpus.
> >=20
> > We can avoid that by only allocating the number of pacas we need at
> > boot. However this is complicated by the fact that we need to access
> > the paca before we know how many cpus there are in the system.
> >=20
> > The solution is to dynamically allocate enough space for NR_CPUS pacas,
> > but then later in boot when we know how many cpus we have, we free any
> > unused pacas.
> >=20
> > Lightly booted on Legacy iSeries & pSeries LPAR.
>=20
> This is broken on 32bit CPUs.  Dies at compile time with
> mpc86xx_defconfig.  No paca on 32bit :-(

Bah, who really uses 32-bit anyway ..

cheers

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