linux-kernel - Re: [PATCH v2 01/11] kexec: introduce kexec

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Date:	Fri, 23 Nov 2012 09:56:52 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	<andrew.cooper3@...rix.com>, <x86@...nel.org>,
	<tglx@...utronix.de>, <kexec@...ts.infradead.org>,
	<virtualization@...ts.linux-foundation.org>,
	<xen-devel@...ts.xensource.com>,
	"Daniel Kiper" <daniel.kiper@...cle.com>, <konrad.wilk@...cle.com>,
	<mingo@...hat.com>, <linux-kernel@...r.kernel.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: [PATCH v2 01/11] kexec: introduce kexec_ops struct

>>> On 22.11.12 at 18:37, "H. Peter Anvin" <hpa@...or.com> wrote:
> I actually talked to Ian Jackson at LCE, and mentioned among other 
> things the bogosity of requiring a PUD page for three-level paging in 
> Linux -- a bogosity which has spread from Xen into native.  It's a page 
> wasted for no good reason, since it only contains 32 bytes worth of 
> data, *inherently*.  Furthermore, contrary to popular belief, it is 
> *not* pa page table per se.
> 
> Ian told me: "I didn't know we did that, and we shouldn't have to." 
> Here we have suffered this overhead for at least six years, ...

Even the Xen kernel only needs the full page when running on a
64-bit hypervisor (now that we don't have a 32-bit hypervisor
anymore, that of course basically means always). But yes, I too
never liked this enforced over-allocation for native kernels (and
was surprised that it was allowed in at all).

Jan

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