linux-kernel - Re: remap allocator for per-CPU memory

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Message-Id: <4A0AEAC80200007800000BC3@vpn.id2.novell.com>
Date:	Wed, 13 May 2009 14:44:08 +0100
From:	"Jan Beulich" <JBeulich@...ell.com>
To:	"Tejun Heo" <TeHeo@...ell.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>, "Andi Kleen" <andi@...stfloor.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: remap allocator for per-CPU memory

>>> Tejun Heo <teheo@...ell.com> 13.05.09 15:29 >>>
>> (b) teach the pageattr code to handle the per-CPU virtual area similarly to
>> the kernel space for x86-64 (though it's going to be a little more complicated
>> since there's no pre-determined relation between the virtual and physical
>> addresses - the necessary lookup might become expensive on systems with
>> very many [possible] CPUs).
>
>Can you elaborate this a bit?  Let's sya there's quick way to match
>whether the page is part of the remapped large page, what can pageattr
>do differently then?  Applying the same attribute to both mappings?
>Failing or filtering set_memory_*()?

It would have to split the page. Perhaps there wouldn't be a need to apply the
new attribute to the page(s) that is(are) in the process of getting its(their)
attribute(s) changed; instead, just don't re-establish a 4k mapping for those
pages that aren't part of the per-CPU space.

And of course, the request should fail when it targets one of the pages that
are actually part of the per-CPU space -- but would be a BUG() anyway.

Jan

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