linux-kernel - Re: [PATCH] [RESEND] x86_64: add memory hotremove config option

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Message-ID: <20080908113025.GF26079@one.firstfloor.org>
Date:	Mon, 8 Sep 2008 13:30:25 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Yasunori Goto <y-goto@...fujitsu.com>,
	Gary Hade <garyhade@...ibm.com>, linux-mm@...ck.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Badari Pulavarty <pbadari@...ibm.com>,
	Mel Gorman <mel@....ul.ie>, Chris McDermott <lcm@...ibm.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] [RESEND] x86_64: add memory hotremove config option

> Sorry, by "block", I really mean spin I guess. I mean that the CPU will
> be forced to stop executing due to the page fault during this sequence:

It's hard for NMIs at least. They cannot execute faults.

In the end you would need to define a core kernel which 
cannot be remapped and the rest which can and you end up
with even more micro kernel like mess.

> ptep_clear_flush(ptep)         <--- from here
> set_pte(ptep, newpte)          <--- until here
> 
> for prot RW, the window also would include the memcpy, however if that
> adds too much latency for execute/reads, then it can be mapped RO first,
> then memcpy, then flushed and switched.
>  
> 
> > Then that would be essentially a hypervisor or micro kernel approach.
> 
> What would be? Blocking in interrupts? Or non-linear kernel mapping in

Well in general someone remapping all the memory beyond you.
That's essentially a hypervisor in my book.

-Andi
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