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

On 20.06.2017 18:44, Rik van Riel wrote:

On Mon, 2017-06-12 at 07:10 -0700, Dave Hansen wrote:

quoted

The hypervisor is going to throw away the contents of these pages,
right?  As soon as the spinlock is released, someone can allocate a
page, and put good data in it.  What keeps the hypervisor from
throwing
away good data?

That looks like it may be the wrong API, then?

We already have hooks called arch_free_page and
arch_alloc_page in the VM, which are called when
pages are freed, and allocated, respectively.

Nitesh Lal (on the CC list) is working on a way
to efficiently batch recently freed pages for
free page hinting to the hypervisor.

If that is done efficiently enough (eg. with
MADV_FREE on the hypervisor side for lazy freeing,
and lazy later re-use of the pages), do we still
need the harder to use batch interface from this
patch?

David's opinion incoming:

No, I think proper free page hinting would be the optimum solution, if
done right. This would avoid the batch interface and even turn
virtio-balloon in some sense useless.

-- 

Thanks,

David