Re: [RFC PATCH v5 0/8] Make balloon drivers' memory changes known to the rest of the kernel

["Denis V. Lunev" <den@virtuozzo.com>]

On 10/19/22 12:53, Konstantin Khlebnikov wrote:
> On Wed, 19 Oct 2022 at 12:57, Alexander Atanasov 
> <alexander.atanasov@virtuozzo.com> wrote:
>
>     Currently balloon drivers (Virtio,XEN, HyperV, VMWare, ...)
>     inflate and deflate the guest memory size but there is no
>     way to know how much the memory size is changed by them.
>
>     Make it possible for the drivers to report the values to mm core.
>
>     Display reported InflatedTotal and InflatedFree in /proc/meminfo
>     and print these values on OOM and sysrq from show_mem().
>
>     The two values are the result of the two modes the drivers work
>     with using adjust_managed_page_count or without.
>
>     In earlier versions, there was a notifier for these changes
>     but after discussion - it is better to implement it in separate
>     patch series. Since it came out as larger work than initially
>     expected.
>
>     Amount of inflated memory can be used:
>      - totalram_pages() users working with drivers not using
>         adjust_managed_page_count
>      - si_meminfo(..) users can improve calculations
>      - by userspace software that monitors memory pressure
>
>
> Sorry, I see no reason for that series.
> Balloon inflation adjusts totalram_pages. That's enough.
>
no, they are not at least under some circumstances, f.e.
virtio balloon does not do that with VIRTIO_BALLOON_F_DEFLATE_ON_OOM
set

> There is no reason to know the amount of non-existent ballooned memory 
> inside.
> Management software which works outside should care about that.
>
The problem comes at the moment when we are running
our Linux server inside virtual machine and the customer
comes with crazy questions "where our memory?".

> For debugging you could get current balloon size from /proc/vmstat 
> (balloon_inflate - balloon_deflate).
> Also (I guess) /proc/kpageflags has a bit for that.
>
> Anyway it's easy to monitor balloon inflation by seeing changes of 
> total memory size.
for monitoring - may be. But in order to report total amount
there is no interface so far.

>
>     Alexander Atanasov (8):
>       mm: Make a place for a common balloon code
>       mm: Enable balloon drivers to report inflated memory
>       mm: Display inflated memory to users
>       mm: Display inflated memory in logs
>       drivers: virtio: balloon - report inflated memory
>       drivers: vmware: balloon - report inflated memory
>       drivers: hyperv: balloon - report inflated memory
>       documentation: create a document about how balloon drivers operate
>
>      Documentation/filesystems/proc.rst            |   6 +
>      Documentation/mm/balloon.rst                  | 138
>     ++++++++++++++++++
>      MAINTAINERS                                   |   4 +-
>      arch/powerpc/platforms/pseries/cmm.c          |   2 +-
>      drivers/hv/hv_balloon.c                       |  12 ++
>      drivers/misc/vmw_balloon.c                    |   3 +-
>      drivers/virtio/virtio_balloon.c               |   7 +-
>      fs/proc/meminfo.c                             |  10 ++
>      .../linux/{balloon_compaction.h => balloon.h} |  18 ++-
>      lib/show_mem.c                                |   8 +
>      mm/Makefile                                   |   2 +-
>      mm/{balloon_compaction.c => balloon.c}        |  19 ++-
>      mm/migrate.c                                  |   1 -
>      mm/vmscan.c                                   |   1 -
>      14 files changed, 213 insertions(+), 18 deletions(-)
>      create mode 100644 Documentation/mm/balloon.rst
>      rename include/linux/{balloon_compaction.h => balloon.h} (91%)
>      rename mm/{balloon_compaction.c => balloon.c} (94%)
>
>     v4->v5:
>      - removed notifier
>      - added documentation
>      - vmware update after op is done , outside of the mutex
>     v3->v4:
>      - add support in hyperV and vmware balloon drivers
>      - display balloon memory in show_mem so it is logged on OOM and
>     on sysrq
>     v2->v3:
>      - added missed EXPORT_SYMBOLS
>     Reported-by: kernel test robot <lkp@intel.com>
>      - instead of balloon_common.h just use balloon.h (yes, naming is
>     hard)
>      - cleaned up balloon.h - remove from files that do not use it and
>        remove externs from function declarations
>     v1->v2:
>      - reworked from simple /proc/meminfo addition
>
>     Cc: Michael S. Tsirkin <mst@redhat.com>
>     Cc: David Hildenbrand <david@redhat.com>
>     Cc: Wei Liu <wei.liu@kernel.org>
>     Cc: Nadav Amit <namit@vmware.com>
>     Cc: pv-drivers@vmware.com
>     Cc: Jason Wang <jasowang@redhat.com>
>     Cc: virtualization@lists.linux-foundation.org
>     Cc: "K. Y. Srinivasan" <kys@microsoft.com>
>     Cc: Haiyang Zhang <haiyangz@microsoft.com>
>     Cc: Stephen Hemminger <sthemmin@microsoft.com>
>     Cc: Dexuan Cui <decui@microsoft.com>
>     Cc: linux-hyperv@vger.kernel.org
>     Cc: Juergen Gross <jgross@suse.com>
>     Cc: Stefano Stabellini <sstabellini@kernel.org>
>     Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
>     Cc: xen-devel@lists.xenproject.org
>
>     base-commit: 9abf2313adc1ca1b6180c508c25f22f9395cc780
>     -- 
>     2.31.1
>