KSM and HugePages

KSM and HugePages

[David Martin]

Does KSM support HugePages?  Reading the Fedora 12 feature list I notice this:
"Using huge pages for guest memory does have a downside, however - you
can no longer swap nor balloon guest memory."
However it is unclear to me if that includes KSM.

If I use 1GB HugePages and KSM (assuming this is possible), does that
mean the entire 1GB page has to match another for them to merge?  Are
there any other downsides to using them other than swapping and
ballooning?

Re: KSM and HugePages

[Dor Laor]

On 10/23/2009 08:21 PM, David Martin wrote:
> Does KSM support HugePages?  Reading the Fedora 12 feature list I notice this:
> "Using huge pages for guest memory does have a downside, however - you
> can no longer swap nor balloon guest memory."
> However it is unclear to me if that includes KSM.

ksm pages are only standard 4k pages.

>
> If I use 1GB HugePages and KSM (assuming this is possible), does that
> mean the entire 1GB page has to match another for them to merge?  Are
> there any other downsides to using them other than swapping and
> ballooning?

It needs to be available at VM creation time.
Also the tlb size for use pages is smaller although it does bring better 
results than 4k pages.

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