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

[Ed Swierk]

On Fri, Oct 7, 2016 at 6:46 AM, Frank Myhr <address@hidden> wrote:
> On 10/07/2016 06:56 AM, Alberto Garcia wrote:
>>
>> I would like to know what's the use case you (Frank, Ed)
>> are thinking about:
>
>
>> - Are we talking about command-line options, QMP, or both?
>
>
> Command-line options alone are sufficient for my use case, which is 
> configuring and starting VMs using libvirt.
>
>
>> - Do you know the size of the disk image or you want to be able to set
>>   the cache size without having access to that information? In other
>>   words, what's preventing you from calculating the cache size that you
>>   need?
>
>
> 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.

--Ed