This series provides an asynchronous means of reporting free guest pages to QEMU through virtio-balloon so that the memory associated with those pages can be discarded and reused by other processes and/or guests on the host. Using this it is possible to avoid unnecessary I/O to disk and greatly improve performance in the case of memory overcommit on the host.
As a part of enabling this feature it was necessary to implement the page poison reporting feature which had been added to the kernel, but was not available in QEMU. This patch set adds it as a new device property "page-poison" which is enabled by default, and adds support for migrating the reported value. I originally submitted this patch series back on February 11th 2020[1], but at that time I was focused primarily on the kernel portion of this patch set. However as of April 7th those patches are now included in Linus's kernel tree[2] and so I am submitting the QEMU pieces for inclusion. [1]: https://lore.kernel.org/lkml/20200211224416.29318.44077.stgit@localhost.localdomain/ [2]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b0c504f154718904ae49349147e3b7e6ae91ffdc Changes from v17: Fixed typo in patch 1 title Addressed white-space issues reported via checkpatch Added braces {} for two if statements to match expected coding style Changes from v18: Updated patches 2 and 3 based on input from dhildenb Added comment to patch 2 describing what keeps us from reporting a bad page Added patch to address issue with ROM devices being directly writable Changes from v19: Added std-headers change to match changes pushed for linux kernel headers Added patch to remove "report" from page hinting code paths Updated comment to better explain why we disable hints w/ page poisoning Removed code that was modifying config size for poison vs hinting Dropped x-page-poison property Added code to bounds check the reported region vs the RAM block Dropped patch for ROM devices as that was already pulled in by Paolo Changes from v20: Rearranged patches to push Linux header sync patches to front Removed association between free page hinting and VIRTIO_BALLOON_F_PAGE_POISON Added code to enable VIRTIO_BALLOON_F_PAGE_POISON if page reporting is enabled Fixed possible resource leak if poison or qemu_balloon_is_inhibited return true Changes from v21: Added ack for patch 3 Rewrote patch description for page poison reporting feature Made page-poison independent property and set to enabled by default Added logic to migrate poison_val Added several comments in code to better explain features Switched free-page-reporting property to disabled by default --- Alexander Duyck (5): linux-headers: Update to allow renaming of free_page_report_cmd_id linux-headers: update to contain virito-balloon free page reporting virtio-balloon: Replace free page hinting references to 'report' with 'hint' virtio-balloon: Implement support for page poison reporting feature virtio-balloon: Provide an interface for free page reporting hw/virtio/virtio-balloon.c | 170 ++++++++++++++++++----- include/hw/virtio/virtio-balloon.h | 23 ++- include/standard-headers/linux/virtio_balloon.h | 12 +- 3 files changed, 155 insertions(+), 50 deletions(-) --
