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

[Wei Wang <wei.w.wang@intel.com>]

On 03/17/2017 05:28 AM, Andrew Morton wrote:
> On Thu, 16 Mar 2017 15:08:46 +0800 Wei Wang <wei.w.wang@intel.com> wrote:
>
> > From: Liang Li <liang.z.li@intel.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