This patch series enhances the existing virtio-balloon with the following new features: 1) fast ballooning: transfer ballooned pages between the guest and host in chunks using sgs, instead of one by one; and 2) free_page_vq: a new virtqueue to report guest free pages to the host.
The second feature can be used to accelerate live migration of VMs. Here are some details: Live migration needs to transfer the VM's memory from the source machine to the destination round by round. For the 1st round, all the VM's memory is transferred. From the 2nd round, only the pieces of memory that were written by the guest (after the 1st round) are transferred. One method that is popularly used by the hypervisor to track which part of memory is written is to write-protect all the guest memory. The second feature enables the optimization of the 1st round memory transfer - the hypervisor can skip the transfer of guest free pages in the 1st round. It is not concerned that the memory pages are used after they are given to the hypervisor as a hint of the free pages, because they will be tracked by the hypervisor and transferred in the next round if they are used and written. Change Log: v13->v14: 1) xbitmap: move the code from lib/radix-tree.c to lib/xbitmap.c. 2) xbitmap: consolidate the implementation of xb_bit_set/clear/test into one xb_bit_ops. 3) xbitmap: add documents for the exported APIs. 4) mm: rewrite the function to walk through free page blocks. 5) virtio-balloon: when reporting a free page blcok to the device, if the vq is full (less likey to happen in practice), just skip reporting this block, instead of busywaiting till an entry gets released. 6) virtio-balloon: fail the probe function if adding the signal buf in init_vqs fails. v12->v13: 1) mm: use a callback function to handle the the free page blocks from the report function. This avoids exposing the zone internal to a kernel module. 2) virtio-balloon: send balloon pages or a free page block using a single sg each time. This has the benefits of simpler implementation with no new APIs. 3) virtio-balloon: the free_page_vq is used to report free pages only (no multiple usages interleaving) 4) virtio-balloon: Balloon pages and free page blocks are sent via input sgs, and the completion signal to the host is sent via an output sg. v11->v12: 1) xbitmap: use the xbitmap from Matthew Wilcox to record ballooned pages. 2) virtio-ring: enable the driver to build up a desc chain using vring desc. 3) virtio-ring: Add locking to the existing START_USE() and END_USE() macro to lock/unlock the vq when a vq operation starts/ends. 4) virtio-ring: add virtqueue_kick_sync() and virtqueue_kick_async() 5) virtio-balloon: describe chunks of ballooned pages and free pages blocks directly using one or more chains of desc from the vq. v10->v11: 1) virtio_balloon: use vring_desc to describe a chunk; 2) virtio_ring: support to add an indirect desc table to virtqueue; 3) virtio_balloon: use cmdq to report guest memory statistics. v9->v10: 1) mm: put report_unused_page_block() under CONFIG_VIRTIO_BALLOON; 2) virtio-balloon: add virtballoon_validate(); 3) virtio-balloon: msg format change; 4) virtio-balloon: move miscq handling to a task on system_freezable_wq; 5) virtio-balloon: code cleanup. v8->v9: 1) Split the two new features, VIRTIO_BALLOON_F_BALLOON_CHUNKS and VIRTIO_BALLOON_F_MISC_VQ, which were mixed together in the previous implementation; 2) Simpler function to get the free page block. v7->v8: 1) Use only one chunk format, instead of two. 2) re-write the virtio-balloon implementation patch. 3) commit changes 4) patch re-org Matthew Wilcox (1): lib/xbitmap: Introduce xbitmap Wei Wang (4): lib/xbitmap: add xb_find_next_bit() and xb_zero() virtio-balloon: VIRTIO_BALLOON_F_SG mm: support reporting free page blocks virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ drivers/virtio/virtio_balloon.c | 324 +++++++++++++++++++++++++++++++----- include/linux/mm.h | 6 + include/linux/radix-tree.h | 3 + include/linux/xbitmap.h | 64 +++++++ include/uapi/linux/virtio_balloon.h | 2 + lib/Makefile | 2 +- lib/radix-tree.c | 22 ++- lib/xbitmap.c | 215 ++++++++++++++++++++++++ mm/page_alloc.c | 44 +++++ 9 files changed, 640 insertions(+), 42 deletions(-) create mode 100644 include/linux/xbitmap.h create mode 100644 lib/xbitmap.c -- 2.7.4
