Re: [PATCH] mmu_notifier, kvm: Introduce dirty bit tracking in spteand mmu notifier to help KSM dirty bit tracking

[Rik van Riel]

On 06/22/2011 07:37 PM, Nai Xia wrote:

> On 2MB pages, I'd like to remind you and Rik that ksmd currently splits
> huge pages before their sub pages gets really merged to stable tree.

Your proposal appears to add a condition that causes ksmd to skip
doing that, which can cause the system to start using swap instead
of sharing memory.

> So when there are many 2MB pages each having a 4kB subpage
> changed for all time, this is already a concern for ksmd to judge
> if it's worthwhile to split 2MB page and get its sub-pages merged.
> I think the policy for ksmd in a system should be "If you cannot do sth good,
> at least do nothing evil". So I really don't think we can satisfy _all_ people.
> Get a general method and give users one or two knobs to tune it when they
> are the corner cases. How do  you think of my proposal ?

I think your proposal makes sense for 4kB pages, but the ksmd
policy for 2MB pages probably needs to be much more aggressive.

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