[PATCH 13/17] virDomainMigrate: Introduce VIR_MIGRATE_NON_SHARED_SYNCHRONOUS_WRITES flag

[Ján Tomko]

On a Friday in 2021, Peter Krempa wrote:
>Non-shared storage migration of guests which are disk I/O intensive and
>have fast local storage may actually never converge if the guest happens
>to dirty the disk faster than it can be copied.
>
>This patch introduces a new flag
>'VIR_MIGRATE_NON_SHARED_SYNCHRONOUS_WRITES' which will instruct
>hypervisors to synchronize local I/O writes with the writes to remote
>storage used for migration so that the guest can't overwhelm the
>migration. This comes at a cost of decreased local I/O performance for
>guests which behave well on average.
>
>Signed-off-by: Peter Krempa <pkrempa at redhat.com>
>---
> docs/manpages/virsh.rst          |  6 +++++-
> include/libvirt/libvirt-domain.h | 10 ++++++++++
> src/libvirt-domain.c             | 20 ++++++++++++++++++++
> tools/virsh-domain.c             | 13 +++++++++++++
> 4 files changed, 48 insertions(+), 1 deletion(-)
>
>diff --git a/docs/manpages/virsh.rst b/docs/manpages/virsh.rst
>index 7c50388216..1ce3e77c9f 100644
>--- a/docs/manpages/virsh.rst
>+++ b/docs/manpages/virsh.rst
>@@ -3180,7 +3180,7 @@ migrate
>       [--postcopy-bandwidth bandwidth]
>       [--parallel [--parallel-connections connections]]
>       [--bandwidth bandwidth] [--tls-destination hostname]
>-      [--disks-uri URI]
>+      [--disks-uri URI] [--copy-storage-synchronous-writes]
>
> Migrate domain to another host.  Add *--live* for live migration; <--p2p>
> for peer-2-peer migration; *--direct* for direct migration; or *--tunnelled*
>@@ -3202,6 +3202,10 @@ images on source host to the images found at the same place on the destination
> host. By default only non-shared non-readonly images are transferred. Use
> *--migrate-disks* to explicitly specify a list of disk targets to
> transfer via the comma separated ``disk-list`` argument.
>+With *--copy-storage-synchronous-writes* flag used the disk data migration will
>+synchronous handle guest disk writes to both the original soure and the

synchronously

>+destination to ensure that the disk migration coverges at the price of possibly

converges

>+decreased burst performance.
>
> *--change-protection* enforces that no incompatible configuration changes will
> be made to the domain while the migration is underway; this flag is implicitly

Jano
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