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From: "Wang, Wei W" <wei.w.wang@intel.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: "virtio-dev@lists.oasis-open.org"
	<virtio-dev@lists.oasis-open.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"virtualization@lists.linux-foundation.org"
	<virtualization@lists.linux-foundation.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"mhocko@kernel.org" <mhocko@kernel.org>,
	"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
	"pbonzini@redhat.com" <pbonzini@redhat.com>,
	"liliang.opensource@gmail.com" <liliang.opensource@gmail.com>,
	"yang.zhang.wz@gmail.com" <yang.zhang.wz@gmail.com>,
	"quan.xu0@gmail.com" <quan.xu0@gmail.com>,
	"nilal@redhat.com" <nilal@redhat.com>,
	"riel@redhat.com" <riel@redhat.com>,
	"huangzhichao@huawei.com" <huangzhichao@huawei.com>
Subject: RE: [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT
Date: Fri, 6 Apr 2018 00:11:22 +0000	[thread overview]
Message-ID: <286AC319A985734F985F78AFA26841F7394A9BC3@shsmsx102.ccr.corp.intel.com> (raw)
In-Reply-To: <20180405212850-mutt-send-email-mst@kernel.org>

On Friday, April 6, 2018 2:30 AM, Michael S. Tsirkin wrote:
> On Thu, Apr 05, 2018 at 03:47:28PM +0000, Wang, Wei W wrote:
> > On Thursday, April 5, 2018 10:04 PM, Michael S. Tsirkin wrote:
> > > On Thu, Apr 05, 2018 at 02:05:03AM +0000, Wang, Wei W wrote:
> > > > 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
> > >
> > > The comparison is done in one thread, the update in another one.
> >
> > I think this isn't something that could be solved by adding a lock,
> > unless host waits for the driver's ACK about finishing the update
> > (this is not agreed in the QEMU part discussion).
> >
> > Actually virtio_balloon has F_IOMMU_PLATFORM disabled, maybe we
> don't
> > need to worry about that using DMA api case (we only have gpa added to
> > the vq, and having some entries stay in the vq seems fine). For this
> > feature, I think it would not work with F_IOMMU enabled either.
> 
> Adding a code comment explaining all this might be a good idea.

Thanks, will do.

Best,
Wei

  reply	other threads:[~2018-04-06  0:38 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-03 16:10 [PATCH v30 0/4] Virtio-balloon: support free page reporting Wei Wang
2018-04-03 16:10 ` [PATCH v30 1/4] mm: support reporting free page blocks Wei Wang
2018-04-03 16:10 ` [PATCH v30 2/4] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT Wei Wang
2018-04-03 18:47   ` Michael S. Tsirkin
2018-04-04  2:07     ` Wei Wang
2018-04-04 14:07       ` Michael S. Tsirkin
2018-04-05  0:30         ` Wang, Wei W
2018-04-05  1:12           ` Michael S. Tsirkin
2018-04-05  2:05             ` Wang, Wei W
2018-04-05 14:03               ` Michael S. Tsirkin
2018-04-05 15:47                 ` Wang, Wei W
2018-04-05 18:30                   ` Michael S. Tsirkin
2018-04-06  0:11                     ` Wang, Wei W [this message]
2018-04-03 16:10 ` [PATCH v30 3/4] mm/page_poison: expose page_poisoning_enabled to kernel modules Wei Wang
2018-04-03 16:10 ` [PATCH v30 4/4] virtio-balloon: VIRTIO_BALLOON_F_PAGE_POISON Wei Wang

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