On Tue, Jun 26, 2012 at 7:56 PM, Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote: > On Wed, 27 Jun 2012 00:41:06 +0300, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: >> On Tue, Jun 26, 2012 at 01:32:58PM -0700, Frank Swiderski wrote: >> > This implementation of a virtio balloon driver uses the page cache to >> > "store" pages that have been released to the host. The communication >> > (outside of target counts) is one way--the guest notifies the host when >> > it adds a page to the page cache, allowing the host to madvise(2) with >> > MADV_DONTNEED. Reclaim in the guest is therefore automatic and implicit >> > (via the regular page reclaim). This means that inflating the balloon >> > is similar to the existing balloon mechanism, but the deflate is >> > different--it re-uses existing Linux kernel functionality to >> > automatically reclaim. >> > >> > Signed-off-by: Frank Swiderski <fes@xxxxxxxxxx> >> >> I'm pondering this: >> >> Should it really be a separate driver/device ID? >> If it behaves the same from host POV, maybe it >> should be up to the guest how to inflate/deflate >> the balloon internally? > > Well, it shouldn't steal ID 10, either way :) Either use a completely > bogus number, or ask for an id. > > But AFAICT this should be a an alternate driver of for the same device: > it's not really a separate device, is it? > > Cheers, > Rusty. Apologies, Rusty. Asking for an ID is in the virtio spec, and I completely neglected that step. Though as you and others have pointed out, this probably fits better as a different driver for the same device. Since it changes whether or not the deflate operation is necessary, it also seems that how this should look is different behavior based on a feature bit in the device. If that sounds reasonable, then what I'll do with this patch is merge it with the existing virtio balloon driver with a feature bit for determining which behavior to use. I also think the idea of a generic balloon that the different balloon drivers use for the inflate/deflate operations is interesting and useful, though I think the suggestion of pending that until later is correct. Sounds reasonable? Regards, fes -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
