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 dropped 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.
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 Changes from v22: Added ack for patches 4 & 5 Added additional comment fixes in patch 3 to remove "reporting" reference Renamed rvq in patch 5 to reporting_vq to better match linux kernel Moved call adding reporting_vq to after free_page_vq Changes from v23: Rebased on latest QEMU Dropped patches 1 & 2 as Linux kernel headers were synced Added compat machine code for page-poison feature Changes from v24: Moved free page hinting rename to end of set as feature may be removed entirely Added code to cleanup reporting_vq --- Alexander Duyck (3): virtio-balloon: Implement support for page poison reporting feature virtio-balloon: Provide an interface for free page reporting virtio-balloon: Replace free page hinting references to 'report' with 'hint' hw/core/machine.c | 4 + hw/virtio/virtio-balloon.c | 179 ++++++++++++++++++++++++++++-------- include/hw/virtio/virtio-balloon.h | 23 ++--- 3 files changed, 155 insertions(+), 51 deletions(-) --
