Re: [PATCH 0/8] KVM: Reduce mmu_lock hold time when zapping mmu pages

[Takuya Yoshikawa <takuya.yoshikawa@gmail.com>]

On Wed, 23 Jan 2013 18:44:52 +0800
Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com> wrote:

> On 01/23/2013 06:12 PM, Takuya Yoshikawa wrote:
> > This patch set mitigates another mmu_lock hold time issue.  Although
> > this is not enough and I'm thinking of additional work already, this
> > alone can reduce the lock hold time to some extent.
> > 
> 
> It is not worth doing this kind of complex thing, usually, only a few pages on
> the invalid list. The *really* heavily case is kvm_mmu_zap_all() which can be speeded
> up by using generation number, this is a todo work in kvm wiki:

I don't think this is so complex.  This is a basic programming technique
using linked lists.

The current code which deletes the two link nodes in different functions
looks unnatural to me: traversing the sp->link nodes forces us to break
the loop and sp->hash_link nodes alone is allowed to continue ...

Making each function semantically clear should be more important than
other things.

But maybe a matter of taste, so I'll wait for the maintainers' comments.

> http://www.linux-kvm.org/page/TODO: O(1) mmu invalidation using a generation number
> 
> I am doing this work for some weeks and will post the patch out during these days.

I remember that Avi originally wrote the idea of introducing the
generation of mmu pages in his other work.

Thanks,
	Takuya