Re: Live memory allocation?

Avi Kivity
2009-03-30T13:48:41Z

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).

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