linux-kernel - Re: [Xen-devel] [PATCH 1/2] xen: prepare p2m list for memory hotplug

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Message-ID: <550AF6BA.7060209@citrix.com>
Date:	Thu, 19 Mar 2015 16:18:02 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Juergen Gross <jgross@...e.com>, <linux-kernel@...r.kernel.org>,
	<xen-devel@...ts.xensource.com>, <konrad.wilk@...cle.com>,
	<david.vrabel@...rix.com>, <boris.ostrovsky@...cle.com>,
	<daniel.kiper@...cle.com>
Subject: Re: [Xen-devel] [PATCH 1/2] xen: prepare p2m list for memory hotplug

On 19/03/15 14:31, Juergen Gross wrote:
> Commit 054954eb051f35e74b75a566a96fe756015352c8 ("xen: switch to linear
> virtual mapped sparse p2m list") introduced a regression regarding to
> memory hotplug for a pv-domain: as the virtual space for the p2m list
> is allocated for the to be expected memory size of the domain only,
> hotplugged memory above that size will not be usable by the domain.
> 
> Correct this by using a configurable size for the p2m list in case of
> memory hotplug enabled (default supported memory size is 512 GB for
> 64 bit domains and 4 GB for 32 bit domains).
[...]
> --- a/arch/x86/xen/p2m.c
> +++ b/arch/x86/xen/p2m.c
> @@ -91,6 +91,17 @@ EXPORT_SYMBOL_GPL(xen_p2m_size);
>  unsigned long xen_max_p2m_pfn __read_mostly;
>  EXPORT_SYMBOL_GPL(xen_max_p2m_pfn);
>  
> +#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
> +#ifdef CONFIG_X86_32
> +BUILD_BUG_ON_MSG(CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT > 64)
> +#endif
> +#define P2M_LIMIT max(xen_max_p2m_pfn,					\
> +	((unsigned long)((u64)CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT *	\
> +	1024 * 1024 * 1024 / PAGE_SIZE)))
> +#else
> +#define P2M_LIMIT xen_max_p2m_pfn
> +#endif

Can you arrange the #ifdef's to set xen_max_p2m_pfn to the right value
instead of introducing P2M_LIMIT?

David
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