linux-kernel - Re: [PATCH v1 6/6] virtio-balloon: Add support for aerating memory via hinting

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Date:   Thu, 18 Jul 2019 16:37:44 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     Nitesh Narayan Lal <nitesh@...hat.com>,
        kvm list <kvm@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>,
        Dave Hansen <dave.hansen@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yang Zhang <yang.zhang.wz@...il.com>, pagupta@...hat.com,
        Rik van Riel <riel@...riel.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        lcapitulino@...hat.com, wei.w.wang@...el.com,
        Andrea Arcangeli <aarcange@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>, dan.j.williams@...el.com,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Subject: Re: [PATCH v1 6/6] virtio-balloon: Add support for aerating memory
 via hinting

On Thu, Jul 18, 2019 at 01:29:14PM -0700, Alexander Duyck wrote:
> So one thing that is still an issue then is that my approach would
> only work on the first migration. The problem is the logic I have
> implemented assumes that once we have hinted on a page we don't need
> to do it again. However in order to support migration you would need
> to reset the hinting entirely and start over again after doing a
> migration.

Well with precopy at least it's simple: just clear the
dirty bit, it won't be sent, and then on destination
you get a zero page and later COW on first write.
Right?

With precopy it is tricker as destination waits until it gets
all of memory. I think we could use some trick to
make source pretend it's a zero page, that is cheap to send.

-- 
MST