Re: [RFC for Linux v4 0/2] virtio_balloon: Add VIRTIO_BALLOON_F_CONT_PAGES to report continuous pages

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

On Thu, Jul 16, 2020 at 10:41:50AM +0800, Hui Zhu wrote:
> The first, second and third version are in [1], [2] and [3].
> Code of current version for Linux and qemu is available in [4] and [5].
> Update of this version:
> 1. Report continuous pages will increase the speed.  So added deflate
>    continuous pages.
> 2. According to the comments from David in [6], added 2 new vqs inflate_cont_vq
>    and deflate_cont_vq to report continuous pages with format 32 bits pfn and 32
>    bits size.
> Following is the introduction of the function.
> These patches add VIRTIO_BALLOON_F_CONT_PAGES to virtio_balloon. With this
> flag, balloon tries to use continuous pages to inflate and deflate.
> Opening this flag can bring two benefits:
> 1. Report continuous pages will increase memory report size of each time
>    call tell_host.  Then it will increase the speed of balloon inflate and
>    deflate.
> 2. Host THPs will be splitted when qemu release the page of balloon inflate.
>    Inflate balloon with continuous pages will let QEMU release the pages
>    of same THPs.  That will help decrease the splitted THPs number in
>    the host.
>    Following is an example in a VM with 1G memory 1CPU.  This test setups an
>    environment that has a lot of fragmentation pages.  Then inflate balloon will
>    split the THPs.
> // This is the THP number before VM execution in the host.
> // None use THP.
> cat /proc/meminfo | grep AnonHugePages:
> AnonHugePages:         0 kB
> // After VM start, use usemem
> // (https://git.kernel.org/pub/scm/linux/kernel/git/wfg/vm-scalability.git)
> // punch-holes function generates 400m fragmentation pages in the guest
> // kernel.
> usemem --punch-holes -s -1 800m &
> // This is the THP number after this command in the host.
> // Some THP is used by VM because usemem will access 800M memory
> // in the guest.
> cat /proc/meminfo | grep AnonHugePages:
> AnonHugePages:    911360 kB
> // Connect to the QEMU monitor, setup balloon, and set it size to 600M.
> (qemu) device_add virtio-balloon-pci,id=balloon1
> (qemu) info balloon
> balloon: actual=1024
> (qemu) balloon 600
> (qemu) info balloon
> balloon: actual=600
> // This is the THP number after inflate the balloon in the host.
> cat /proc/meminfo | grep AnonHugePages:
> AnonHugePages:     88064 kB
> // Set the size back to 1024M in the QEMU monitor.
> (qemu) balloon 1024
> (qemu) info balloon
> balloon: actual=1024
> // Use usemem to increase the memory usage of QEMU.
> killall usemem
> usemem 800m
> // This is the THP number after this operation.
> cat /proc/meminfo | grep AnonHugePages:
> AnonHugePages:     65536 kB
> 
> Following example change to use continuous pages balloon.  The number of
> splitted THPs is decreased.
> // This is the THP number before VM execution in the host.
> // None use THP.
> cat /proc/meminfo | grep AnonHugePages:
> AnonHugePages:         0 kB
> // After VM start, use usemem punch-holes function generates 400M
> // fragmentation pages in the guest kernel.
> usemem --punch-holes -s -1 800m &
> // This is the THP number after this command in the host.
> // Some THP is used by VM because usemem will access 800M memory
> // in the guest.
> cat /proc/meminfo | grep AnonHugePages:
> AnonHugePages:    911360 kB
> // Connect to the QEMU monitor, setup balloon, and set it size to 600M.
> (qemu) device_add virtio-balloon-pci,id=balloon1,cont-pages=on
> (qemu) info balloon
> balloon: actual=1024
> (qemu) balloon 600
> (qemu) info balloon
> balloon: actual=600
> // This is the THP number after inflate the balloon in the host.
> cat /proc/meminfo | grep AnonHugePages:
> AnonHugePages:    616448 kB
> // Set the size back to 1024M in the QEMU monitor.
> (qemu) balloon 1024
> (qemu) info balloon
> balloon: actual=1024
> // Use usemem to increase the memory usage of QEMU.
> killall usemem
> usemem 800m
> // This is the THP number after this operation.
> cat /proc/meminfo | grep AnonHugePages:
> AnonHugePages:    907264 kB

I'm a bit confused about which of the above run within guest,
and which run within host. Could you explain pls?



> [1] https://lkml.org/lkml/2020/3/12/144
> [2] https://lore.kernel.org/linux-mm/1584893097-12317-1-git-send-email-teawater@gmail.com/
> [3] https://lkml.org/lkml/2020/5/12/324
> [4] https://github.com/teawater/linux/tree/balloon_conts
> [5] https://github.com/teawater/qemu/tree/balloon_conts
> [6] https://lkml.org/lkml/2020/5/13/1211
> 
> Hui Zhu (2):
>   virtio_balloon: Add VIRTIO_BALLOON_F_CONT_PAGES and inflate_cont_vq
>   virtio_balloon: Add deflate_cont_vq to deflate continuous pages
> 
>  drivers/virtio/virtio_balloon.c     |  180 +++++++++++++++++++++++++++++++-----
>  include/linux/balloon_compaction.h  |   12 ++
>  include/uapi/linux/virtio_balloon.h |    1
>  mm/balloon_compaction.c             |  117 +++++++++++++++++++++--
>  4 files changed, 280 insertions(+), 30 deletions(-)