Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Thu, 18 Jul 2019 16:37:44 -0400
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     Alexander Duyck <alexander.duyck@gmail.com>
Cc:     Nitesh Narayan Lal <nitesh@redhat.com>,
        kvm list <kvm@vger.kernel.org>,
        David Hildenbrand <david@redhat.com>,
        Dave Hansen <dave.hansen@intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Yang Zhang <yang.zhang.wz@gmail.com>, pagupta@redhat.com,
        Rik van Riel <riel@surriel.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        lcapitulino@redhat.com, wei.w.wang@intel.com,
        Andrea Arcangeli <aarcange@redhat.com>,
        Paolo Bonzini <pbonzini@redhat.com>, dan.j.williams@intel.com,
        Alexander Duyck <alexander.h.duyck@linux.intel.com>
Subject: Re: [PATCH v1 6/6] virtio-balloon: Add support for aerating memory
 via hinting
Message-ID: <20190718163325-mutt-send-email-mst@kernel.org>
References: <20190716115535-mutt-send-email-mst@kernel.org>
 <CAKgT0Ud47-cWu9VnAAD_Q2Fjia5gaWCz_L9HUF6PBhbugv6tCQ@mail.gmail.com>
 <20190716125845-mutt-send-email-mst@kernel.org>
 <CAKgT0UfgPdU1H5ZZ7GL7E=_oZNTzTwZN60Q-+2keBxDgQYODfg@mail.gmail.com>
 <20190717055804-mutt-send-email-mst@kernel.org>
 <CAKgT0Uf4iJxEx+3q_Vo9L1QPuv9PhZUv1=M9UCsn6_qs7rG4aw@mail.gmail.com>
 <20190718003211-mutt-send-email-mst@kernel.org>
 <CAKgT0UfQ3dtfjjm8wnNxX1+Azav6ws9zemH6KYc7RuyvyFo3fQ@mail.gmail.com>
 <20190718113548-mutt-send-email-mst@kernel.org>
 <CAKgT0UeRy2eHKnz4CorefBAG8ro+3h4oFX+z1JY2qRm17fcV8w@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAKgT0UeRy2eHKnz4CorefBAG8ro+3h4oFX+z1JY2qRm17fcV8w@mail.gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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