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

[Konstantin Khlebnikov <koct9i@xxxxxxxxx>]

On Wed, 19 Oct 2022 at 14:06, Denis V. Lunev <den@xxxxxxxxxxxxx> wrote:

On 10/19/22 12:53, Konstantin Khlebnikov wrote:
> On Wed, 19 Oct 2022 at 12:57, Alexander Atanasov
> <alexander.atanasov@xxxxxxxxxxxxx> 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?".

Ok. In this case balloon management is partially inside VM.

I.e. we could report portion of balloon as potentially available memory.

I guess memory pressure could deflate balloon till some threshold set by external hypervisor.

So, without knowledge about this threshold there is no correct answer about size of available memory.

Showing just size of balloon doesn't gives much.

 

> 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@xxxxxxxxx>
>      - 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@xxxxxxxxxx>
>     Cc: David Hildenbrand <david@xxxxxxxxxx>
>     Cc: Wei Liu <wei.liu@xxxxxxxxxx>
>     Cc: Nadav Amit <namit@xxxxxxxxxx>
>     Cc: pv-drivers@xxxxxxxxxx
>     Cc: Jason Wang <jasowang@xxxxxxxxxx>
>     Cc: virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx
>     Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
>     Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
>     Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
>     Cc: Dexuan Cui <decui@xxxxxxxxxxxxx>
>     Cc: linux-hyperv@xxxxxxxxxxxxxxx
>     Cc: Juergen Gross <jgross@xxxxxxxx>
>     Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
>     Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
>     Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx
>
>     base-commit: 9abf2313adc1ca1b6180c508c25f22f9395cc780
>     --
>     2.31.1
>