Re: [PATCH v8 0/7] mm / virtio: Provide support for unused page reporting

[Alexander Duyck]

On Fri, Sep 6, 2019 at 8:23 AM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> On Fri, Sep 06, 2019 at 07:53:21AM -0700, Alexander Duyck wrote:
> > This series provides an asynchronous means of reporting to a hypervisor
> > that a guest page is no longer in use and can have the data associated
> > with it dropped. To do this I have implemented functionality that allows
> > for what I am referring to as unused page reporting
> >
> > The functionality for this is fairly simple. When enabled it will allocate
> > statistics to track the number of reported pages in a given free area.
> > When the number of free pages exceeds this value plus a high water value,
> > currently 32, it will begin performing page reporting which consists of
> > pulling pages off of free list and placing them into a scatter list. The
> > scatterlist is then given to the page reporting device and it will perform
> > the required action to make the pages "reported", in the case of
> > virtio-balloon this results in the pages being madvised as MADV_DONTNEED
> > and as such they are forced out of the guest. After this they are placed
> > back on the free list, and an additional bit is added if they are not
> > merged indicating that they are a reported buddy page instead of a
> > standard buddy page. The cycle then repeats with additional non-reported
> > pages being pulled until the free areas all consist of reported pages.
> >
> > I am leaving a number of things hard-coded such as limiting the lowest
> > order processed to PAGEBLOCK_ORDER, and have left it up to the guest to
> > determine what the limit is on how many pages it wants to allocate to
> > process the hints. The upper limit for this is based on the size of the
> > queue used to store the scattergather list.
>
> I queued this  so this gets tested on linux-next but the mm core changes
> need acks from appropriate people.

Thanks. I will see what I can do to get some more mm people reviewing
these changes.

- Alex