Re: [virtio-dev] [PATCH v13 0/5] Virtio-balloon Enhancement

[Adam Tao]

On Thu, Aug 03, 2017 at 02:38:14PM +0800, Wei Wang wrote:
> 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.
> 
Hi wei,
The reason we add the new vq for the migration feature is based on
what(original design based on inflate and deflate vq)?
I am wondering if we add new feature in the future do we still need to add new type
of vq?
Do we need to add one command queue for the common purpose(including
different type of requests except the in/deflate ones)?
Thanks
Adam
> 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:
> 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):
>   Introduce xbitmap
> 
> Wei Wang (4):
>   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     | 302 +++++++++++++++++++++++++++++++-----
>  include/linux/mm.h                  |   7 +
>  include/linux/mmzone.h              |   5 +
>  include/linux/radix-tree.h          |   2 +
>  include/linux/xbitmap.h             |  53 +++++++
>  include/uapi/linux/virtio_balloon.h |   2 +
>  lib/radix-tree.c                    | 167 +++++++++++++++++++-
>  mm/page_alloc.c                     | 109 +++++++++++++
>  8 files changed, 609 insertions(+), 38 deletions(-)
>  create mode 100644 include/linux/xbitmap.h
> 
> -- 
> 2.7.4
> 
> 
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