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

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Date:	Thu, 19 Mar 2015 18:05:48 +0100
From:	Juergen Gross <jgross@...e.com>
To:	Daniel Kiper <daniel.kiper@...cle.com>
CC:	linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com,
	konrad.wilk@...cle.com, david.vrabel@...rix.com,
	boris.ostrovsky@...cle.com
Subject: Re: [PATCH 1/2] xen: prepare p2m list for memory hotplug

On 03/19/2015 05:14 PM, Daniel Kiper wrote:
> On Thu, Mar 19, 2015 at 03:31:01PM +0100, 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  | 13 ++++++++++++-
>>   drivers/xen/Kconfig | 13 +++++++++++++
>>   2 files changed, 25 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
>> index 9f93af5..30e84ae 100644
>> --- 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
>> +
>>   static DEFINE_SPINLOCK(p2m_update_lock);
>>
>>   static unsigned long *p2m_mid_missing_mfn;
>> @@ -387,7 +398,7 @@ void __init xen_vmalloc_p2m_tree(void)
>>   	static struct vm_struct vm;
>>
>>   	vm.flags = VM_ALLOC;
>> -	vm.size = ALIGN(sizeof(unsigned long) * xen_max_p2m_pfn,
>> +	vm.size = ALIGN(sizeof(unsigned long) * P2M_LIMIT,
>>   			PMD_SIZE * PMDS_PER_MID_PAGE);
>
> What happens when somebody will allocate more memory for guest than
> XEN_BALLOON_MEMORY_HOTPLUG_LIMIT? Additionally, I think that we do

It will fail to add like it does without this patch.

> not need allocate extra virtual address space if memory hotplug is
> disabled.

As XEN_BALLOON_MEMORY_HOTPLUG_LIMIT depends on
XEN_BALLOON_MEMORY_HOTPLUG which in turn depends on MEMORY_HOTPLUG,
this is already the case.

>
>>   	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..0a61ddf 100644
>> --- a/drivers/xen/Kconfig
>> +++ b/drivers/xen/Kconfig
>> @@ -55,6 +55,19 @@ config XEN_BALLOON_MEMORY_HOTPLUG
>>
>>   	  In that case step 3 should be omitted.
>>
>> +config XEN_BALLOON_MEMORY_HOTPLUG_LIMIT
>> +	int
>> +	default 512 if X86_64
>> +	default 4 if X86_32
>> +	depends on XEN_HAVE_PVMMU
>
> Do we need dependency on XEN_HAVE_PVMMU?

Yes. Needed only for pv domains.

> If yes than maybe "depends on XEN_HAVE_PVMMU && XEN_BALLOON_MEMORY_HOTPLUG".

Matter of taste, I guess.

>
>> +	depends on XEN_BALLOON_MEMORY_HOTPLUG
>
> Should not this option be available even when memory hotplug is disabled?

Why?


Juergen
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