linux-kernel - Re: [PATCH] adjust/fix LDT handling for Xen

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Date:	Mon, 14 Jan 2008 08:22:06 +0000
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Jeremy Fitzhardinge" <Jeremy.Fitzhardinge@...rix.com>
Cc:	"Ingo Molnar" <mingo@...e.hu>, <linux-kernel@...r.kernel.org>,
	"Jeremy Fitzhardinge" <jeremy@...source.com>
Subject: Re: [PATCH] adjust/fix LDT handling for Xen

>>> Jeremy Fitzhardinge <Jeremy.Fitzhardinge@...rix.com> 11.01.08 18:28 >>>
>Jan Beulich wrote:
>> Don't rely on kmalloc(PAGE_SIZE) returning PAGE_SIZE aligned memory
>> (Xen requires GDT *and* LDT to be page-aligned).
>
>Can kmalloc return non-page-aligned PAGE_SIZE allocations?

Documentation says it's to return pointer-size aligned memory - any excess
alignment is therefore an implementation detail. (Nevertheless, afaics all
current allocators generate page-aligned chunks.)

>>  Using the page
>> allocator interface also removes the (albeit small) slab allocator
>> overhead.
>
>Runtime or space overhead?  Given that they're once-off allocations, the 
>time part isn't a big factor.  And apparently LDT is completely unused.

Both, but as I also said the saving is small.

Jan

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