linux-kernel - RE: [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE

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Date:   Thu, 5 Apr 2018 02:05:03 +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>,
        "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>,
        "huangzhichao@...wei.com" <huangzhichao@...wei.com>
Subject: RE: [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT

On Thursday, April 5, 2018 9:12 AM, Michael S. Tsirkin wrote:
> On Thu, Apr 05, 2018 at 12:30:27AM +0000, Wang, Wei W wrote:
> > On Wednesday, April 4, 2018 10:08 PM, Michael S. Tsirkin wrote:
> > > On Wed, Apr 04, 2018 at 10:07:51AM +0800, Wei Wang wrote:
> > > > On 04/04/2018 02:47 AM, Michael S. Tsirkin wrote:
> > > > > On Wed, Apr 04, 2018 at 12:10:03AM +0800, Wei Wang wrote:
> > I'm afraid the driver couldn't be aware if the added hints are stale
> > or not,
> 
> 
> No - I mean that driver has code that compares two values and stops
> reporting. Can one of the values be stale?

The driver compares "vb->cmd_id_use != vb->cmd_id_received" to decide if it needs to stop reporting hints, and cmd_id_received is what the driver reads from host (host notifies the driver to read for the latest value). If host sends a new cmd id, it will notify the guest to read again. I'm not sure how that could be a stale cmd id (or maybe I misunderstood your point here?)

Best,
Wei