Re: [virtio-dev] [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 03:01:18PM +0800, teawater wrote:
> 
> 
> > 2020年7月16日 14:38，Michael S. Tsirkin <mst@redhat.com> 写道：
> > 
> > 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
> These lines are from host.
> 
> >> // 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 &
> These lines are from guest.  They setups the environment that has a lot of fragmentation pages.
> 
> >> // 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
> These lines are from host.
> 
> >> // 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
> These lines are from host.
> 
> >> // This is the THP number after inflate the balloon in the host.
> >> cat /proc/meminfo | grep AnonHugePages:
> >> AnonHugePages:     88064 kB
> These lines are from host.
> 
> >> // Set the size back to 1024M in the QEMU monitor.
> >> (qemu) balloon 1024
> >> (qemu) info balloon
> >> balloon: actual=1024
> These lines are from host.
> 
> >> // Use usemem to increase the memory usage of QEMU.
> >> killall usemem
> >> usemem 800m
> These lines are from guest.
> 
> >> // This is the THP number after this operation.
> >> cat /proc/meminfo | grep AnonHugePages:
> >> AnonHugePages:     65536 kB
> These lines are from host.
> 
> 
> 
> >> 
> >> 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
> These lines are from host.
> 
> >> // After VM start, use usemem punch-holes function generates 400M
> >> // fragmentation pages in the guest kernel.
> >> usemem --punch-holes -s -1 800m &
> These lines are from guest.  They setups the environment that has a lot of fragmentation pages.
> 
> >> // 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
> These lines are from host.
> 
> >> // 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
> These lines are from host.
> 
> >> // 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
> These lines are from host.
> 
> >> // Use usemem to increase the memory usage of QEMU.
> >> killall usemem
> >> usemem 800m
> These lines are from guest.
> 
> >> // This is the THP number after this operation.
> >> cat /proc/meminfo | grep AnonHugePages:
> >> AnonHugePages:    907264 kB
> These lines are from host.
> 
> > 
> > I'm a bit confused about which of the above run within guest,
> > and which run within host. Could you explain pls?
> > 
> > 
> 
> I added some introduction to show where these lines is get from.
> 
> Best,
> Hui


OK so we see host has more free THPs. But guest has presumably less now - so
the total page table depth is the same. Did we gain anything?

> 
> > 
> >> [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(-)
> > 
> > 
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