linux-kernel - Re: [GIT PATCH] x86,percpu: fix pageattr handling with remap allocator

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Date:	Wed, 20 May 2009 16:01:10 -0700
From:	Suresh Siddha <suresh.b.siddha@...el.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	"JBeulich@...ell.com" <JBeulich@...ell.com>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"linux-kernel-owner@...r.kernel.org" 
	<linux-kernel-owner@...r.kernel.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PATCH] x86,percpu: fix pageattr handling with remap
 allocator

On Mon, 2009-05-18 at 18:28 -0700, Tejun Heo wrote:
> Hello, Suresh.
> 
> Suresh Siddha wrote:
> > This %gs:absolute type accesses are for static percpu data.
> > 
> > But what I was referring to is the dynamic percpu data(accessed through
> > per_cpu_ptr()). Instead of combining some part of the dynamic percpu
> > data into  the static percpu data(first percpu chunk), we can use
> > different chunks for dynamic percpu data and governed by a different
> > per_cpu_dynamic_offset[NR_CPUS] array.
> > 
> > Then we can use large-page kernel direct mappings for static percpu data
> > (or %gs:offset) and small-page vmalloc mappings for dynamic percpu data.
> 
> Hmmm... I can't really follow what you're suggesting.  Can you please
> explain it in more detailed way?

Ok. Before I make another attempt walking that hill :)

I was talking to Peter and it seems there are some requests to change
the first percpu unit allocation for each possible cpu using bootmem
allocator, to allocating the corresponding unit at the cpu online time.

Do you have plans to change this? If we do this allocation during the
corresponding cpu online time and don't end up using big pages, then
also we avoid all these aliasing issues...

thanks,
suresh

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