Re: [Qemu-devel] [Qemu-block] [PATCH] qcow2: Optimize L2 table cache size based on image and cluster sizes

[Alberto Garcia]

On Fri 07 Oct 2016 03:58:29 PM CEST, Ed Swierk wrote:

>> I know the disk image size, and can set cache size in
>> bytes. l2-cache-size=max would be a convenience feature, *especially
>> if it could become the default*. Then I could forget thinking about
>> whether the image is larger than the current 8GB fully-cached
>> threshold, and only have to calculate cache size in bytes in case of
>> very large images, multiple backing files, or very tight memory.
>
> Same here, using libvirt. l2-cache-size=max would be ideal. Or if
> there were a cache-coverage-size option that takes an absolute number,
> libvirt could set it to the image size.

I can see the benefit of both approaches: setting the disk size covered
by the cache or setting a percentage, I personally like a bit more the
former but it wouldn't provide a way to say "create the largest cache
needed for this disk".

Would 'l2-cache-coverage-size' work for everyone? It would simply take
the disk size (16G, 1T, etc) and it would conflict with l2-cache-size.

Do we need something similar for the refcount cache?

Berto