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Re: [libvirt] [PATCH 0/2] Add 'l2-cache-size' property to specify maximum size of the L2 table cache for qcow2 image

[Cc: Alberto Garcia of QEMU, who added the 'l2-cache-size' upstream]

On Wed, Nov 15, 2017 at 05:54:13AM -0500, John Ferlan wrote:
> On 11/14/2017 08:58 PM, Lin Ma wrote:
> > Lin Ma (2):
> >   caps: Add capability for maximum size of the qcow2 L2 table cache
> >   qemu: Add support for 'l2-cache-size' property of qcow2
> > 
> There's already something on list about l2 cache, see
> https://www.redhat.com/archives/libvir-list/2017-September/msg00553.html
> it adds 3 related variables. IIRC, the "hold up" is how best to describe
> how to use it or provide the feature in such a way that it's
> "understandable" for general consumption without making a "policy" that
> generates certain values based on expected usage/needs for the client.

I recall Alberto saying that there's a default value of QCOW2
'l2-cache-size', but it is (intentionally?) low.  And that the value
depends on the workload / use case: size of the image, the amount of I/O
you want to do, etc.

There's also an RFE for OpenStack Nova to expose this.  (But I don't
know if it makes sense to expose it at that level, yet.)



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