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

[David Hildenbrand]

On 20.06.2017 18:44, Rik van Riel wrote:
> On Mon, 2017-06-12 at 07:10 -0700, Dave Hansen wrote:
> 
>> 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