linux-kernel - Re: [PATCH kernel v8 3/4] mm: add inerface to offer info about unused pages

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Date:   Thu, 13 Apr 2017 19:07:57 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
CC:     virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org,
        qemu-devel@...gnu.org, virtualization@...ts.linux-foundation.org,
        kvm@...r.kernel.org, linux-mm@...ck.org, mst@...hat.com,
        david@...hat.com, dave.hansen@...el.com, cornelia.huck@...ibm.com,
        mgorman@...hsingularity.net, aarcange@...hat.com,
        amit.shah@...hat.com, pbonzini@...hat.com,
        liliang.opensource@...il.com
Subject: Re: [PATCH kernel v8 3/4] mm: add inerface to offer info about unused
 pages

On 03/17/2017 05:28 AM, Andrew Morton wrote:
> On Thu, 16 Mar 2017 15:08:46 +0800 Wei Wang <wei.w.wang@...el.com> wrote:
>
>> From: Liang Li <liang.z.li@...el.com>
>>
>> This patch adds a function to provides a snapshot of the present system
>> unused pages. An important usage of this function is to provide the
>> unsused pages to the Live migration thread, which skips the transfer of
>> thoses unused pages. Newly used pages can be re-tracked by the dirty
>> page logging mechanisms.
> I don't think this will be useful for anything other than
> virtio-balloon.  I guess it would be better to keep this code in the
> virtio-balloon driver if possible, even though that's rather a layering
> violation :( What would have to be done to make that possible?  Perhaps
> we can put some *small* helpers into page_alloc.c to prevent things
> from becoming too ugly.
>
>
Thanks for the suggestion. Small helpers do look more elegant. The nice 
thing is that I also didn't see any performance loss.
To make that possible, we need to enable for_each_polulated_zone() to be 
callable by a kernel module. Please have a check the v9 patches that I 
just posted out.

Best,
Wei