Re: [Qemu-devel] [QEMU 2/7] virtio-balloon: add drop cache support

[Li, Liang Z]

> On Mon, Jun 13, 2016 at 06:16:44PM +0800, Liang Li wrote:
> > virtio-balloon can make use of the amount of free memory to determine
> > the amount of memory to be filled in the balloon, but the amount of
> > free memory will be effected by the page cache, which can be reclaimed.
> > Drop the cache before getting the amount of free memory will be very
> > helpful to relect the exact amount of memroy that can be reclaimed.
> 
> Can't we just extend stats to report "reclaimable" memory?
> 

Yes, I noticed the VIRTIO_BALLOON_S_AVAIL is for this purpose.  

I summarized the possible solutions from others:
a. Drop the cache in guest agent instead of an obvious qmp command. (Paolo) 
b. Use a parameter as a hint to tell the guest live migration is going to 
happen, and let the guest do what it can do to make the host's life easier.  
(David)

What' your opinion about these two solutions?

Thanks!
Liang