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

["Michael S. Tsirkin" <mst@redhat.com>]

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.

> My primary testing has just been to verify the memory is being freed after
> allocation by running memhog 40g on a 40g 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. I have modified it to use Transparent Huge Pages. With this I
> see almost no difference, -0.08%, with the patches applied and the feature
> disabled. I see a regression of -0.86% with the feature enabled, but the
> madvise disabled in the hypervisor due to a device being assigned. With
> the feature fully enabled I see a regression of -3.27% versus the baseline
> without these patches applied. In my testing I found that most of the
> overhead was due to the page zeroing that comes as a result of the pages
> having to be faulted back into the guest.
> 
> One side effect of these patches is that the guest becomes much more
> resilient in terms of NUMA locality. With the pages being freed and then
> reallocated when used it allows for the pages to be much closer to the
> active thread, and as a result there can be situations where this patch
> set will out-perform the stock kernel when the guest memory is not local
> to the guest vCPUs. To avoid that in my testing I set the affinity of all
> the vCPUs and QEMU instance to the same node.
> 
> Changes from the RFC:
> https://lore.kernel.org/lkml/20190530215223.13974.22445.stgit@localhost.localdomain/
> 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.
> 
> Changes from v1:
> https://lore.kernel.org/lkml/20190619222922.1231.27432.stgit@localhost.localdomain/
> Dropped "waste page treatment" in favor of "page hinting"
> Renamed files and functions from "aeration" to "page_hinting"
> Moved from page->lru list to scatterlist
> Replaced wait on refcnt in shutdown with RCU and cancel_delayed_work_sync
> Virtio now uses scatterlist directly instead of intermediate array
> Moved stats out of free_area, now in separate area and pointed to from zone
> Merged patch 5 into patch 4 to improve review-ability
> Updated various code comments throughout
> 
> Changes from v2:
> https://lore.kernel.org/lkml/20190724165158.6685.87228.stgit@localhost.localdomain/
> Dropped "page hinting" in favor of "page reporting"
> Renamed files from "hinting" to "reporting"
> Replaced "Hinted" page type with "Reported" page flag
> Added support for page poisoning while hinting is active
> Add QEMU patch that implements PAGE_POISON feature
> 
> Changes from v3:
> https://lore.kernel.org/lkml/20190801222158.22190.96964.stgit@localhost.localdomain/
> Added mutex lock around page reporting startup and shutdown
> Fixed reference to "page aeration" in patch 2
> Split page reporting function bit out into separate QEMU patch
> Limited capacity of scatterlist to vq size - 1 instead of vq size
> Added exception handling for case of virtio descriptor allocation failure
> 
> Changes from v4:
> https://lore.kernel.org/lkml/20190807224037.6891.53512.stgit@localhost.localdomain/
> Replaced spin_(un)lock with spin_(un)lock_irq in page_reporting_cycle()
> Dropped if/continue for ternary operator in page_reporting_process()
> Added checks for isolate and cma types to for_each_reporting_migratetype_order
> Added virtio-dev, Michal Hocko, and Oscar Salvador to to:/cc:
> Rebased on latest linux-next and QEMU git trees
> 
> Changes from v5:
> https://lore.kernel.org/lkml/20190812213158.22097.30576.stgit@localhost.localdomain/
> Replaced spin_(un)lock with spin_(un)lock_irq in page_reporting_startup()
> Updated shuffle code to use "shuffle_pick_tail" and updated patch description
> Dropped storage of order and migratettype while page is being reported
> Used get_pfnblock_migratetype to determine migratetype of page
> Renamed put_reported_page to free_reported_page, added order as argument
> Dropped check for CMA type as I believe we should be reporting those
> Added code to allow moving of reported pages into and out of isolation
> Defined page reporting order as minimum of Huge Page size vs MAX_ORDER - 1
> Cleaned up use of static branch usage for page_reporting_notify_enabled
> 
> Changes from v6:
> https://lore.kernel.org/lkml/20190821145806.20926.22448.stgit@localhost.localdomain/
> Rebased on linux-next for 20190903
> Added jump label to __page_reporting_request so we release RCU read lock
> Removed "- 1" from capacity limit based on virtio ring
> Added code to verify capacity is non-zero or return error on startup
> 
> Changes from v7:
> https://lore.kernel.org/lkml/20190904150920.13848.32271.stgit@localhost.localdomain/
> Updated poison fixes to clear flag if "nosanity" is enabled in kernel config
> Split shuffle per-cpu optimization into seperate patch
> Moved check for !phdev->capacity into reporting patch where it belongs
> Added Reviewed-by tags received for v7
> 
> ---
> 
> Alexander Duyck (7):
>       mm: Add per-cpu logic to page shuffling
>       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 Reported pages
>       virtio-balloon: Pull page poisoning config out of free page hinting
>       virtio-balloon: Add support for providing unused page reports to host
> 
> 
>  drivers/virtio/Kconfig              |    1 
>  drivers/virtio/virtio_balloon.c     |   87 ++++++++-
>  include/linux/mmzone.h              |  124 ++++++++-----
>  include/linux/page-flags.h          |   11 +
>  include/linux/page_reporting.h      |  177 ++++++++++++++++++
>  include/uapi/linux/virtio_balloon.h |    1 
>  mm/Kconfig                          |    5 +
>  mm/Makefile                         |    1 
>  mm/internal.h                       |   18 ++
>  mm/memory_hotplug.c                 |    1 
>  mm/page_alloc.c                     |  216 ++++++++++++++++------
>  mm/page_reporting.c                 |  340 +++++++++++++++++++++++++++++++++++
>  mm/shuffle.c                        |   40 ++--
>  mm/shuffle.h                        |   12 +
>  14 files changed, 902 insertions(+), 132 deletions(-)
>  create mode 100644 include/linux/page_reporting.h
>  create mode 100644 mm/page_reporting.c
> 
> --