Subject: Re: [RFC/PATCH] powerpc: Dynamically allocate pacas

From: Michael Neuling <[email-masked]>
Date: Thu, 14 Jan 2010 11:26:22 +1100

> On 64-bit kernels we currently have a 512 byte struct paca_struct for
> each cpu (usually just called "the paca"). Currently they are statically
> 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.
> 
> 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.
> 
> 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.
> 
> Lightly booted on Legacy iSeries & pSeries LPAR.
> 
> Signed-off-by: Michael Ellerman <[email-masked]>

Nice!

<snip>

> +	lmb_free(__pa(paca) + new_size, paca_size - new_size);

You didn't explicitly mention this above but this depends on your
lmb_free patch...

FYI boots bare metal

Mikey