linux-kernel - Re: [RFC][Patch v8 0/7] KVM: Guest Free Page Hinting

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Date:   Tue, 19 Feb 2019 14:58:51 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Nitesh Narayan Lal <nitesh@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>, lcapitulino@...hat.com,
        pagupta@...hat.com, wei.w.wang@...el.com,
        Yang Zhang <yang.zhang.wz@...il.com>,
        Rik van Riel <riel@...riel.com>, dodgen@...gle.com,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        dhildenb@...hat.com, Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [RFC][Patch v8 0/7] KVM: Guest Free Page Hinting

On Tue, Feb 19, 2019 at 10:06:35AM -0800, Alexander Duyck wrote:
> > I tend to like an asynchronous reporting approach as discussed in this
> > thread, we would have to see if Nitesh could get it implemented.
> 
> I agree it would be great if it could work. However I have concerns
> given that work on this patch set dates back to 2017, major issues
> such as working around device assignment have yet to be addressed,

BTW for device assignment to work, your idea of sending
data directly to kvm won't work, will it?
You need to update userspace so it can update VFIO right?
Another blocker for assignment is ability to make holes
an an existing mapping - supported by hardware but
not by IOMMU drivers.

All the issues are shared with balloon btw, so that
could be another reason to use the balloon.

> and
> it seems like most of the effort is being focused on things that in my
> opinion are being over-engineered for little to no benefit.
> 
> I really think that simpler would be much better in terms of design in
> this case.
> 
> Thanks.
> 
> - Alex

I personally learned a lot from Wei's work on hinting.


All this doesn't mean you approach is not the right one.

-- 
MST