linux-kernel - Re: [Xen-devel] [PATCH 10/27] xen: make sure swiotlb allocation isphysically contigious

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Date:	Mon, 16 Mar 2009 13:30:22 +0000
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Jeremy Fitzhardinge" <jeremy@...p.org>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Jeremy Fitzhardinge" <jeremy.fitzhardinge@...rix.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	"David Airlie" <airlied@...ux.ie>,
	"Xen-devel" <xen-devel@...ts.xensource.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 10/27] xen: make sure swiotlb
	 allocation isphysically contigious

>>> Jeremy Fitzhardinge <jeremy@...p.org> 13.03.09 17:59 >>>
> void * __init swiotlb_alloc_boot(size_t size, unsigned long nslabs)
> {
>-	return alloc_bootmem_low_pages(size);
>+	void *ret = alloc_bootmem_low_pages(size);
>+
>+	if (ret && xen_pv_domain())
>+		xen_swiotlb_fixup(ret, size, nslabs);
>+
>+	return ret;
> }
 
While on native using alloc_bootmem_low_pages() is a requirement here,
on Xen this should explicitly not be used, as we realized just a couple of
days ago: The way the bootmem allocator works, running out of space
below 4Gb is pretty easy on machines with lots of memory, and since the
swiotlb is a requirement for Dom0, the risk of allocation failures must be
kept as low as possible.

Jan

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