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

Alexander Duyck
2019-06-19T22:33:02Z

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 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
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.

---

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

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