linux-kernel - RE: [PATCH v33 0/4] Virtio-balloon: support free page reporting

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Date:   Fri, 15 Jun 2018 14:28:49 +0000
From:   "Wang, Wei W" <wei.w.wang@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     "virtio-dev@...ts.oasis-open.org" <virtio-dev@...ts.oasis-open.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "liliang.opensource@...il.com" <liliang.opensource@...il.com>,
        "yang.zhang.wz@...il.com" <yang.zhang.wz@...il.com>,
        "quan.xu0@...il.com" <quan.xu0@...il.com>,
        "nilal@...hat.com" <nilal@...hat.com>,
        "riel@...hat.com" <riel@...hat.com>,
        "peterx@...hat.com" <peterx@...hat.com>
Subject: RE: [PATCH v33 0/4] Virtio-balloon: support free page reporting

On Friday, June 15, 2018 7:30 PM, Michael S. Tsirkin wrote:
> On Fri, Jun 15, 2018 at 12:43:09PM +0800, Wei Wang wrote:
> >       - remove the cmd id related interface. Now host can just send a free
> >         page hint command to the guest (via the host_cmd config register)
> >         to start the reporting.
> 
> Here we go again. And what if reporting was already started previously?
> I don't think it's a good idea to tweak the host/guest interface yet again.

This interface is much simpler, and I'm not sure if that would be an issue here now, because
now the guest delivers the whole buffer of hints to host once, instead of hint by hint as before. And the guest notifies host after the buffer is delivered. In any case, the host doorbell handler will be invoked, if host doesn't need the hints at that time, it will just give back the buffer. There will be no stale hints remained in the ring now.

Best,
Wei