linux-kernel - Re: [PATCH v11 4/6] mm: function to offer a page block on the free list

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Message-ID: <9d0900f3-9df5-ac63-4069-2d796f2a5bc7@intel.com>
Date:   Mon, 12 Jun 2017 09:42:36 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     Wei Wang <wei.w.wang@...el.com>, linux-kernel@...r.kernel.org,
        qemu-devel@...gnu.org, virtualization@...ts.linux-foundation.org,
        kvm@...r.kernel.org, linux-mm@...ck.org, david@...hat.com,
        cornelia.huck@...ibm.com, akpm@...ux-foundation.org,
        mgorman@...hsingularity.net, aarcange@...hat.com,
        amit.shah@...hat.com, pbonzini@...hat.com,
        liliang.opensource@...il.com
Subject: Re: [PATCH v11 4/6] mm: function to offer a page block on the free
 list

On 06/12/2017 09:28 AM, Michael S. Tsirkin wrote:
> 
>> The hypervisor is going to throw away the contents of these pages,
>> right?
> It should be careful and only throw away contents that was there before
> report_unused_page_block was invoked.  Hypervisor is responsible for not
> corrupting guest memory.  But that's not something an mm patch should
> worry about.

That makes sense.  I'm struggling to imagine how the hypervisor makes
use of this information, though.  Does it make the pages read-only
before this, and then it knows if there has not been a write *and* it
gets notified via this new mechanism that it can throw the page away?