lkml.org 
[lkml]   [2020]   [Jan]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Subject[PATCH v16 0/9] mm / virtio: Provide support for free page reporting
    From
    Date
    This series provides an asynchronous means of reporting free guest pages
    to a hypervisor so that the memory associated with those pages can be
    dropped and reused by other processes and/or guests on the host. Using
    this it is possible to avoid unnecessary I/O to disk and greatly improve
    performance in the case of memory overcommit on the host.

    When enabled we will be performing a scan of free memory every 2 seconds
    while pages of sufficiently high order are being freed. In each pass at
    least one sixteenth of each free list will be reported. By doing this we
    avoid racing against other threads that may be causing a high amount of
    memory churn.

    The lowest page order currently scanned when reporting pages is
    pageblock_order so that this feature will not interfere with the use of
    Transparent Huge Pages in the case of virtualization.

    Currently this is only in use by virtio-balloon however there is the hope
    that at some point in the future other hypervisors might be able to make
    use of it. In the virtio-balloon/QEMU implementation the hypervisor is
    currently using MADV_DONTNEED to indicate to the host kernel that the page
    is currently free. It will be zeroed and faulted back into the guest the
    next time the page is accessed.

    To track if a page is reported or not the Uptodate flag was repurposed and
    used as a Reported flag for Buddy pages. We walk though the free list
    isolating pages and adding them to the scatterlist until we either
    encounter the end of the list, processed as many pages as were listed in
    nr_free prior to us starting, or have filled the scatterlist with pages to
    be reported. If we fill the scatterlist before we reach the end of the
    list we rotate the list so that the first unreported page we encounter is
    moved to the head of the list as that is where we will resume after we
    have freed the reported pages back into the tail of the list.

    Below are the results from various benchmarks. I primarily focused on two
    tests. The first is the will-it-scale/page_fault2 test, and the other is
    a modified version of will-it-scale/page_fault1 that was enabled to use
    THP. I did this as it allows for better visibility into different parts
    of the memory subsystem. The guest is running with 32G for RAM on one
    node of a E5-2630 v3. The host has had some features such as CPU turbo
    disabled in the BIOS.

    Test page_fault1 (THP) page_fault2
    Name tasks Process Iter STDEV Process Iter STDEV
    Baseline 1 1012402.50 0.14% 361855.25 0.81%
    16 8827457.25 0.09% 3282347.00 0.34%

    Patches Applied 1 1007897.00 0.23% 361887.00 0.26%
    16 8784741.75 0.39% 3240669.25 0.48%

    Patches Enabled 1 1010227.50 0.39% 359749.25 0.56%
    16 8756219.00 0.24% 3226608.75 0.97%

    Patches Enabled 1 1050982.00 4.26% 357966.25 0.14%
    page shuffle 16 8672601.25 0.49% 3223177.75 0.40%

    Patches Enabled 1 1003238.00 0.22% 360211.00 0.22%
    shuffle w/ RFC 16 8767010.50 0.32% 3199874.00 0.71%

    The results above are for a baseline with a linux-next-20191219 kernel,
    that kernel with this patch set applied but page reporting disabled in
    virtio-balloon, the patches applied and page reporting fully enabled, the
    patches enabled with page shuffling enabled, and the patches applied with
    page shuffling enabled and an RFC patch that makes used of MADV_FREE in
    QEMU. These results include the deviation seen between the average value
    reported here versus the high and/or low value. I observed that during the
    test memory usage for the first three tests never dropped whereas with the
    patches fully enabled the VM would drop to using only a few GB of the
    host's memory when switching from memhog to page fault tests.

    Any of the overhead visible with this patch set enabled seems due to page
    faults caused by accessing the reported pages and the host zeroing the page
    before giving it back to the guest. This overhead is much more visible when
    using THP than with standard 4K pages. In addition page shuffling seemed to
    increase the amount of faults generated due to an increase in memory churn.
    The overhead is reduced when using MADV_FREE as we can avoid the extra
    zeroing of the pages when they are reintroduced to the host, as can be seen
    when the RFC is applied with shuffling enabled.

    The overall guest size is kept fairly small to only a few GB while the test
    is running. If the host memory were oversubscribed this patch set should
    result in a performance improvement as swapping memory in the host can be
    avoided.

    A brief history on the background of free page reporting can be found at:
    https://lore.kernel.org/lkml/29f43d5796feed0dec8e8bb98b187d9dac03b900.camel@linux.intel.com/

    Changes from v14:
    https://lore.kernel.org/lkml/20191119214454.24996.66289.stgit@localhost.localdomain/
    Renamed "unused page reporting" to "free page reporting"
    Updated code, kconfig, and patch descriptions
    Split out patch for __free_isolated_page
    Renamed function to __putback_isolated_page
    Rewrote core reporting functionality
    Added logic to reschedule worker in 2 seconds instead of run to completion
    Removed reported_pages statistics
    Removed REPORTING_REQUESTED bit used in zone flags
    Replaced page_reporting_dev_info refcount with state variable
    Removed scatterlist from page_reporting_dev_info
    Removed capacity from page reporting device
    Added dynamic scatterlist allocation/free at start/end of reporting process
    Updated __free_one_page so that reported pages are not always added to tail
    Added logic to handle error from report function
    Updated virtio-balloon patch that adds support for page reporting
    Updated patch description to try and highlight differences in approaches
    Updated logic to reflect that we cannot limit the scatterlist from device
    Added logic to return error from report function
    Moved documentation patch to end of patch set

    Changes from v15:
    https://lore.kernel.org/lkml/20191205161928.19548.41654.stgit@localhost.localdomain/
    Rebased on linux-next-20191219
    Split out patches for budget and moving head to last page processed
    Updated budget code to reduce how much memory is reported per pass
    Added logic to also rotate the list if we exit due a page isolation failure
    Added migratetype as argument in __putback_isolated_page

    ---

    Alexander Duyck (9):
    mm: Adjust shuffle code to allow for future coalescing
    mm: Use zone and order instead of free area in free_list manipulators
    mm: Add function __putback_isolated_page
    mm: Introduce Reported pages
    virtio-balloon: Pull page poisoning config out of free page hinting
    virtio-balloon: Add support for providing free page reports to host
    mm: Rotate free list so reported pages are moved to the tail of the list
    mm: Add budget limit to how many pages can be reported per list per pass
    mm: Add free page reporting documentation


    Documentation/vm/free_page_reporting.rst | 41 +++
    drivers/virtio/Kconfig | 1
    drivers/virtio/virtio_balloon.c | 87 +++++++
    include/linux/mmzone.h | 44 ----
    include/linux/page-flags.h | 11 +
    include/linux/page_reporting.h | 26 ++
    include/uapi/linux/virtio_balloon.h | 1
    mm/Kconfig | 11 +
    mm/Makefile | 1
    mm/internal.h | 2
    mm/page_alloc.c | 164 ++++++++++----
    mm/page_isolation.c | 6
    mm/page_reporting.c | 364 ++++++++++++++++++++++++++++++
    mm/page_reporting.h | 54 ++++
    mm/shuffle.c | 12 -
    mm/shuffle.h | 6
    16 files changed, 725 insertions(+), 106 deletions(-)
    create mode 100644 Documentation/vm/free_page_reporting.rst
    create mode 100644 include/linux/page_reporting.h
    create mode 100644 mm/page_reporting.c
    create mode 100644 mm/page_reporting.h

    --

    \
     
     \ /
      Last update: 2020-01-03 22:17    [W:7.673 / U:0.304 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site