Re: [Xen-devel] [PATCH v4 00/20] xen/arm64: Add support for 64KB page in Linux

[David Vrabel <david.vrabel@xxxxxxxxxx>]

On 14/09/15 12:32, Arnd Bergmann wrote:
> On Monday 14 September 2015 13:04:59 Roger Pau Monné wrote:
>>> TBH, I'm expecting a small impact to the performance. It would be hard
>>> to get the exactly the same performance as today if we keep the helpers
>>> to avoid the backend dealing himself with the splitting and page
>>> granularity.
>>>
>>> Although, if the performance impact is not acceptable, it may be
>>> possible to optimize gnttab_foreach_grant_in_range by moving the
>>> function inline. The current way to the loop is the fastest I've found
>>> (I've wrote a small program to test different way) and we will need it
>>> when different of size will be supported.
>>
>> I don't expect the performance to drop massively with this patches
>> applied, but it would be good to al least have an idea of the impact.
> 
> Note that using 64kb pages in Linux tends to destroy performance
> in Linux in any case, as the memory consumption for most workloads
> explodes. In a virtualized environment you already tend to be
> memory constrained, so any measurement should take that into account
> and put the extra overhead into perspective to the massive overhead
> of running 64kb pages when RAM is tight.

If this is the case, why are some distros using 64 KiB pages then?

David

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