linux-kernel - Re: [Xen-devel] [Patch V2 1/2] xen: prepare p2m list for memory hotplug

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Date:	Mon, 23 Mar 2015 15:29:16 +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, pebolle@...cali.nl
Subject: Re: [Xen-devel] [Patch V2 1/2] xen: prepare p2m list for memory hotplug

On 03/23/2015 01:46 PM, David Vrabel wrote:
> On 20/03/15 12:55, 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).
>>
>> Signed-off-by: Juergen Gross <jgross@...e.com>
>> ---
>>   arch/x86/xen/p2m.c  | 10 +++++++++-
>>   drivers/xen/Kconfig | 14 ++++++++++++++
>>   2 files changed, 23 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
>> index 9f93af5..b47124d 100644
>> --- a/arch/x86/xen/p2m.c
>> +++ b/arch/x86/xen/p2m.c
>> @@ -91,6 +91,12 @@ 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
>> +#define P2M_LIMIT CONFIG_XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
>> +#else
>> +#define P2M_LIMIT 0
>> +#endif
>> +
>>   static DEFINE_SPINLOCK(p2m_update_lock);
>>
>>   static unsigned long *p2m_mid_missing_mfn;
>> @@ -385,9 +391,11 @@ static void __init xen_rebuild_p2m_list(unsigned long *p2m)
>>   void __init xen_vmalloc_p2m_tree(void)
>>   {
>>   	static struct vm_struct vm;
>> +	unsigned long p2m_limit;
>>
>> +	p2m_limit = (phys_addr_t)P2M_LIMIT * 1024 * 1024 * 1024 / PAGE_SIZE;
>>   	vm.flags = VM_ALLOC;
>> -	vm.size = ALIGN(sizeof(unsigned long) * xen_max_p2m_pfn,
>> +	vm.size = ALIGN(sizeof(unsigned long) * max(xen_max_p2m_pfn, p2m_limit),
>>   			PMD_SIZE * PMDS_PER_MID_PAGE);
>>   	vm_area_register_early(&vm, PMD_SIZE * PMDS_PER_MID_PAGE);
>>   	pr_notice("p2m virtual area at %p, size is %lx\n", vm.addr, vm.size);
>> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig
>> index b812462..0f1b509 100644
>> --- a/drivers/xen/Kconfig
>> +++ b/drivers/xen/Kconfig
>> @@ -55,6 +55,20 @@ config XEN_BALLOON_MEMORY_HOTPLUG
>>
>>   	  In that case step 3 should be omitted.
>>
>> +config XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
>> +	int
>
> Because you've not supplied a summary for this option, it is not user
> configurable.  Is this intentional?

No. Sorry, I just tested it via editing .config, not using the menues.
Can you add it when committing (e.g. "Upper limit in GBs a pv domain
can be expanded to using memory hotplug")?

Or should I send another patch?


Juergen
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