Re: [Qemu-devel] [PATCH 3/4] docs: document how to configure the qcow2 L2/refcount caches

[Alberto Garcia]

On Fri 05 Jun 2015 05:52:29 PM CEST, Max Reitz wrote:
>> +Reducing the memory usage
>> +-------------------------
>> +It is possible to clean unused cache entries in order to reduce the
>> +memory usage during periods of low I/O activity.
>> +
>> +The parameter "cache-clean-interval" defines an interval (in seconds)
>> +after which all unused cache entries are removed from memory.
>> +
>> +This example removes all unused cache entries every 15 minutes:
>> +
>> +   -drive file=hd.qcow2,cache-clean-interval=900
>> +
>> +If unset, the default value for this parameter is 0 and it disables
>> +this feature.
>> +
>> +Note that this functionality currently relies on the MADV_DONTNEED
>> +argument for madvise() to actually free the memory, so it is not
>> +useful in systems that don't follow that behavior.
>
> I'd like a definition of what "unused" means (I know because of this
> series, but I wouldn't know just from this document).

It means that it hasn't been accessed in that interval (because it was
not needed). Are you thinking of any other possible interpretation?

Berto