Re: [PATCH v1 0/6] mm / virtio: Provide support for paravirtual waste page treatment

[Alexander Duyck <alexander.duyck@gmail.com>]

On Tue, Jun 25, 2019 at 12:42 AM David Hildenbrand <david@redhat.com> wrote:
>
> On 20.06.19 00:32, Alexander Duyck wrote:
> > This series provides an asynchronous means of hinting 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 waste page treatment.
> >
> > I have based many of the terms and functionality off of waste water
> > treatment, the idea for the similarity occurred to me after I had reached
> > the point of referring to the hints as "bubbles", as the hints used the
> > same approach as the balloon functionality but would disappear if they
> > were touched, as a result I started to think of the virtio device as an
> > aerator. The general idea with all of this is that the guest should be
> > treating the unused pages so that when they end up heading "downstream"
> > to either another guest, or back at the host they will not need to be
> > written to swap.
> >
> > When the number of "dirty" pages in a given free_area exceeds our high
> > water mark, which is currently 32, we will schedule the aeration task to
> > start going through and scrubbing the zone. While the scrubbing is taking
> > place a boundary will be defined that we use to seperate the "aerated"
> > pages from the "dirty" ones. We use the ZONE_AERATION_ACTIVE bit to flag
> > when these boundaries are in place.
>
> I still *detest* the terminology, sorry. Can't you come up with a
> simpler terminology that makes more sense in the context of operating
> systems and pages we want to hint to the hypervisor? (that is the only
> use case you are using it for so far)

I'm open to suggestions. The terminology is just what I went with as I
had gone from balloon to thinking of this as a bubble since it was a
balloon without the deflate logic. From there I got to aeration since
it is filling the buddy allocator with those bubbles.

> >
> > 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 batch size it wants to allocate to process the hints.
> >
> > My primary testing has just been to verify the memory is being freed after
> > allocation by running memhog 32g in the guest and watching the total free
> > memory via /proc/meminfo on the host. With this I have verified most of
> > the memory is freed after each iteration. As far as performance I have
> > been mainly focusing on the will-it-scale/page_fault1 test running with
> > 16 vcpus. With that I have seen a less than 1% difference between the
>
> 1% throughout all benchmarks? Guess that is quite good.

That is the general idea. What I wanted to avoid was this introducing
any significant slowdown, especially in the case where we weren't
using it.

> > base kernel without these patches, with the patches and virtio-balloon
> > disabled, and with the patches and virtio-balloon enabled with hinting.
> >
> > Changes from the RFC:
> > Moved aeration requested flag out of aerator and into zone->flags.
> > Moved boundary out of free_area and into local variables for aeration.
> > Moved aeration cycle out of interrupt and into workqueue.
> > Left nr_free as total pages instead of splitting it between raw and aerated.
> > Combined size and physical address values in virtio ring into one 64b value.
> > Restructured the patch set to reduce patches from 11 to 6.
> >
>
> I'm planning to look into the details, but will be on PTO for two weeks
> starting this Saturday (and still have other things to finish first :/ ).

Thanks. No rush. I will be on PTO for the next couple of weeks myself.

> > ---
> >
> > Alexander Duyck (6):
> >       mm: Adjust shuffle code to allow for future coalescing
> >       mm: Move set/get_pcppage_migratetype to mmzone.h
> >       mm: Use zone and order instead of free area in free_list manipulators
> >       mm: Introduce "aerated" pages
> >       mm: Add logic for separating "aerated" pages from "raw" pages
> >       virtio-balloon: Add support for aerating memory via hinting
> >
> >
> >  drivers/virtio/Kconfig              |    1
> >  drivers/virtio/virtio_balloon.c     |  110 ++++++++++++++
> >  include/linux/memory_aeration.h     |  118 +++++++++++++++
> >  include/linux/mmzone.h              |  113 +++++++++------
> >  include/linux/page-flags.h          |    8 +
> >  include/uapi/linux/virtio_balloon.h |    1
> >  mm/Kconfig                          |    5 +
> >  mm/Makefile                         |    1
> >  mm/aeration.c                       |  270 +++++++++++++++++++++++++++++++++++
> >  mm/page_alloc.c                     |  203 ++++++++++++++++++--------
> >  mm/shuffle.c                        |   24 ---
> >  mm/shuffle.h                        |   35 +++++
> >  12 files changed, 753 insertions(+), 136 deletions(-)
> >  create mode 100644 include/linux/memory_aeration.h
> >  create mode 100644 mm/aeration.c
>
> Compared to
>
>  17 files changed, 838 insertions(+), 86 deletions(-)
>  create mode 100644 include/linux/memory_aeration.h
>  create mode 100644 mm/aeration.c
>
> this looks like a good improvement :)

Thanks.

- Alex