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

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Message-ID: <550B0450.6000209@suse.com>
Date:	Thu, 19 Mar 2015 18:16:00 +0100
From:	Juergen Gross <jgross@...e.com>
To:	David Vrabel <david.vrabel@...rix.com>,
	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	konrad.wilk@...cle.com, boris.ostrovsky@...cle.com,
	daniel.kiper@...cle.com
Subject: Re: [Xen-devel] [PATCH 1/2] xen: prepare p2m list for memory hotplug

On 03/19/2015 05:18 PM, David Vrabel wrote:
> 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?

Hmm, this would require additional checks in setup.c. What about:

#ifdef CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
#define P2M_LIMIT CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
#else
#define P2M_LIMIT 0
#endif

and do the max(...) calculation in xen_vmalloc_p2m_tree()?


Juergen

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