On Thu, May 25, 2023 at 10:20:11PM +0000, T.J. Alumbaugh wrote: > This is the device implementation for the proposed expanded balloon feature > described here: > > https://lore.kernel.org/linux-mm/20230509185419.1088297-1-yuan...@google.com/ > > This series has a fixed number of "bins" for the working set report, but this > is > not a constraint of the system. The bin number is fixed at device realization > time (in other implementations it is specified as a command line argument). > Once > that number is fixed, this determines the correct number of bin intervals to > pass to the QMP/HMP function 'working_set_config'. Any feedback on how to > properly construct that function for this use case (passing a variable length > list?) would be appreciated.
It's been a while. Is there interest is reviving this? I also note that reserving a feature bit is very much recommended to avoid a complete mess. > New in V2: > ========= > > - Patch series is now: header file changes, device changes, QMP changes, HMP > chagnes, and migration changes. > > - Exmaple usages of QMP and HMP interface are in their respective commit > messages. > > - "ws" -> "working_set" throughout > > Motivation > ========== > As mentioned in the above message, the use case is a host with overcommitted > memory and 1 or more VMs. The goal is to get both timely and accurate > information on overall memory utilization in order to drive appropriate > reclaim activities, since in some client device use cases a VM might need a > significant fraction of the overall memory for a period of time, but then > enter a quiet period that results in a large number of cold pages in the > guest. > > The balloon device now has a number of features to assist in sharing memory > resources amongst the guests and host (e.g free page hinting, stats, free page > reporting). As mentioned in slide 12 in [1], the balloon doesn't have a good > mechanism to drive the reclaim of guest cache. Our use case includes both > typical page cache as well as "application caches" with memory that should be > discarded in times of system-wide memory pressure. In some cases, virtio-pmem > can be a method for host control of guest cache but there are undesirable > security implications. > > Working Set Reporting > ===================== > The patch series here includes: > > - Actual device implementation for VIRTIO_F_WS_REPORTING to standardize the > configuration and communication of Working Set reports from the guest. This > includes a notification virtqueue for receiving config information and > requests for a report (a feature which could be expanded for additional use > cases) and a virtqueue for the actual report from the driver. > > - QMP changes so that a controller program can use the existing QEMU socket > mechanism to configure and request WS reports and then read the reports as > a JSON property on the balloon. > > Working Set reporting in the balloon provides: > > - an accurate picture of current memory utilization in the guest > - event driven reporting (with configurable rate limiting) to deliver reports > during times of memory pressure. > > The reporting mechanism can be combined with a domain-specific balloon policy > to drive the separate reclaim activities in a coordinated fashion. > > TODOs: > ====== > - A synchronization mechanism must be added to the functions that send WS > Config and WS Request, otherwise concurrent callers (through QMP) can mix > messages on the virtqueue sending the data to the driver. > > - The device currently has a hard-coded setting of 4 'bins' for a Working Set > report, whereas the specification calls for anywhere between 2 and 16. > > - A WS_EVENT notification through QMP should include the actual report, > whereas right now we query for that information right after a WS_EVENT is > received. > > References: > > [1] > https://kvmforum2020.sched.com/event/eE4U/virtio-balloonpmemmem-managing-guest-memory-david-hildenbrand-michael-s-tsirkin-red-hat > > T.J. Alumbaugh (5): > virtio-balloon: Add Working Set Reporting feature > virtio-balloon: device has Working Set Reporting > virtio-balloon: Add QMP functions for Working Set > virtio-balloon: Add HMP functions for Working Set > virtio-balloon: Migration of working set config > > hmp-commands.hx | 26 ++ > hw/core/machine-hmp-cmds.c | 21 ++ > hw/virtio/virtio-balloon-pci.c | 2 + > hw/virtio/virtio-balloon.c | 239 +++++++++++++++++- > include/hw/virtio/virtio-balloon.h | 13 +- > include/monitor/hmp.h | 2 + > .../standard-headers/linux/virtio_balloon.h | 20 ++ > include/sysemu/balloon.h | 9 +- > monitor/monitor.c | 1 + > qapi/machine.json | 66 +++++ > qapi/misc.json | 26 ++ > softmmu/balloon.c | 31 ++- > 12 files changed, 449 insertions(+), 7 deletions(-) > > -- > 2.41.0.rc0.172.g3f132b7071-goog
