linux-kernel - Re: [PATCH v12 5/8] virtio-balloon: VIRTIO_BALLOON_F

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Date:   Mon, 31 Jul 2017 20:36:09 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "david@...hat.com" <david@...hat.com>,
        "cornelia.huck@...ibm.com" <cornelia.huck@...ibm.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "mgorman@...hsingularity.net" <mgorman@...hsingularity.net>,
        "aarcange@...hat.com" <aarcange@...hat.com>,
        "amit.shah@...hat.com" <amit.shah@...hat.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "liliang.opensource@...il.com" <liliang.opensource@...il.com>,
        "virtio-dev@...ts.oasis-open.org" <virtio-dev@...ts.oasis-open.org>,
        "yang.zhang.wz@...il.com" <yang.zhang.wz@...il.com>,
        "quan.xu@...yun.com" <quan.xu@...yun.com>
Subject: Re: [PATCH v12 5/8] virtio-balloon: VIRTIO_BALLOON_F_SG

On 07/31/2017 12:20 AM, Michael S. Tsirkin wrote:
> On Sun, Jul 30, 2017 at 07:18:33PM +0300, Michael S. Tsirkin wrote:
>> On Sun, Jul 30, 2017 at 05:59:17AM +0000, Wang, Wei W wrote:
>> That's a hypervisor implementation detail. From guest point of view,
>> discarding contents can not be distinguished from writing old contents.
>>
> Besides, ignoring the free page tricks, consider regular ballooning.
> We map page with DONTNEED then back with WILLNEED. Result is
> getting a zero page. So at least one of deflate/inflate should be input.
> I'd say both for symmetry.
>

OK, I see the point. Thanks.

Best,
Wei