linux-kernel - Re: [PATCH v3 1/1] Create debugfs file with hyper-v balloon usage information

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Date:   Mon, 5 Sep 2022 16:20:56 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Cc:     Wei Liu <wei.liu@...nel.org>,
        Alexander Atanasov <alexander.atanasov@...tuozzo.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Dexuan Cui <decui@...rosoft.com>,
        "kernel@...nvz.org" <kernel@...nvz.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/1] Create debugfs file with hyper-v balloon usage
 information

On Sat, Sep 03, 2022 at 04:37:12AM +0000, Michael Kelley (LINUX) wrote:
> From: Wei Liu <wei.liu@...nel.org> Sent: Wednesday, July 13, 2022 8:19 AM
> > 
> > On Tue, Jul 12, 2022 at 04:24:12PM +0000, Michael Kelley (LINUX) wrote:
> > > From: Alexander Atanasov <alexander.atanasov@...tuozzo.com> Sent: Monday, July
> > 11, 2022 11:18 AM
> > > >
> > > > Allow the guest to know how much it is ballooned by the host.
> > > > It is useful when debugging out of memory conditions.
> > > >
> > > > When host gets back memory from the guest it is accounted
> > > > as used memory in the guest but the guest have no way to know
> > > > how much it is actually ballooned.
> > > >
> > > > Expose current state, flags and max possible memory to the guest.
> > > > While at it - fix a 10+ years old typo.
> > > >
> > > > Signed-off-by: Alexander Atanasov <alexander.atanasov@...tuozzo.com>
> > > > ---
> > [...]
> > >
> > > Reviewed-by: Michael Kelley <mikelley@...rosoft.com>
> > 
> > I added "Drivers: hv:" prefix to the subject line and applied it to
> > hyperv-next. Thanks.
> 
> Alexander -- I finally caught up on the long discussion of balloon
> driver reporting that occurred over much of August.  I think your
> original plan had been for each of the balloon driver to report
> useful information in debugfs.  But as a result of the discussion,
> it looks like virtio-balloon will be putting the information in
> /proc/meminfo.  If that's the case, it seems like we should
> drop these changes to the Hyper-V balloon driver,  and have
> the Hyper-V balloon driver take the same approach as
> virtio-balloon.

The debugfs interface contains far more information than what can be put
into meminfo.

That being said, I can send a PR to revert the changes if we need time
to wait for the other discussion to come to an conclusion.

> 
> These Hyper-V balloon driver changes have already gone
> into 6.0-rc1.  If we're going to drop them, we should do
> the revert before 6.0 is done.
> 

Agreed.

Michael, let me know what you think.

Thanks,
Wei.

> Thoughts?
> 
> Michael