Re: Live memory allocation?

Tomasz Chmielewski
2009-03-30T13:55:41Z

Avi Kivity schrieb:
> Tomasz Chmielewski wrote:
>>
>> What about cache/buffers sharing between the host kernel and running
>> processes?
>>
>>
>> If I'm not mistaken, right now, memory is "wasted" by caching the same
>> data by host and guest kernels.
>>
>> For example, let's say we have a host with 2 GB RAM and it runs a 1 GB
>> guest.
>> If we read ~900 MB file_1 (block device) on guest, then:
>> - guest's kernel will cache file_1
>> - host's kernel will cache the same area of file_1 (block device)
>>
>> Now, if we want to read ~900 MB file_2 (or lots of files with that
>> size), cache for file_1 will be emptied on both guest and host as we
>> read file_2.
>> Ideal situation would be if host and guest caches could be "shared",
>> to a degree (and have both file_1 and file_2 in memory, doesn't matter
>> if it's guest or host).
>
> Double caching is indeed a bad idea. That's why you have cache=off
> (though it isn't recommended with qcow2).

cache= option is about write cache, right?

Here, I'm talking about read cache.

Or, does "cache=none" disable read cache as well?

--
Tomasz Chmielewski