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Re: [PATCH v5 0/8] virtio-mem: Handle preallocation with migration
From: |
Michael S. Tsirkin |
Subject: |
Re: [PATCH v5 0/8] virtio-mem: Handle preallocation with migration |
Date: |
Thu, 2 Feb 2023 06:11:11 -0500 |
On Tue, Jan 17, 2023 at 12:22:41PM +0100, David Hildenbrand wrote:
> While playing with migration of virtio-mem with an ordinary file backing,
> I realized that migration and prealloc doesn't currently work as expected
> for virtio-mem. Further, Jing Qi reported that setup issues (insufficient
> huge pages on the destination) result in QEMU getting killed with SIGBUS
> instead of failing gracefully.
>
> In contrast to ordinary memory backend preallocation, virtio-mem
> preallocates memory before plugging blocks to the guest. Consequently,
> when migrating we are not actually preallocating on the destination but
> "only" migrate pages. Fix that be migrating the bitmap early, before any
> RAM content, and use that information to preallocate memory early, before
> migrating any RAM.
>
> Postcopy needs some extra care, and I realized that prealloc+postcopy is
> shaky in general. Let's at least try to mimic what ordinary
> prealloc+postcopy does: temporarily allocate the memory, discard it, and
> cross fingers that we'll still have sufficient memory when postcopy
> actually tries placing pages.
>
> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Cc: Juan Quintela <quintela@redhat.com>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
> v4 -> v5:
> - "migration/savevm: Move more savevm handling into vmstate_save()"
> -- Extended patch description regarding tracing
> - "migration/savevm: Prepare vmdesc json writer in
> qemu_savevm_state_setup()"
> -- Move freeing to migrate_fd_cleanup()
> - "migration/savevm: Allow immutable device state to be migrated early (i.e.,
> before RAM)"
> -- "immutable" -> "early_setup"
> -- Extend comment
> - Added some RBs (thanks!)
>
> v3 -> v4:
> - First 3 patches:
> -- Minimze code changes and simplify
> -- Save immutable device state during qemu_savevm_state_setup()
> -- Don't use vmsd priorities, use a new flag
> -- Split it logically up
> - "migration/ram: Factor out check for advised postcopy"
> -- Don't factor out postcopy_is_running()
> - "virtio-mem: Migrate immutable properties early"
> -- Adjust to changed vmsd interface
> - "virtio-mem: Proper support for preallocation with migration"
> -- Drop sanity check in virtio_mem_post_load_early()
>
> v2 -> v3:
> - New approach/rewrite, drop RB and TB of last patch
>
> v1 -> v2:
> - Added RBs and Tested-bys
> - "virtio-mem: Fail if a memory backend with "prealloc=on" is specified"
> -- Fail instead of warn
> -- Adjust subject/description
>
>
> David Hildenbrand (8):
> migration/savevm: Move more savevm handling into vmstate_save()
> migration/savevm: Prepare vmdesc json writer in
> qemu_savevm_state_setup()
> migration/savevm: Allow immutable device state to be migrated early
> (i.e., before RAM)
> migration/vmstate: Introduce VMSTATE_WITH_TMP_TEST() and
> VMSTATE_BITMAP_TEST()
> migration/ram: Factor out check for advised postcopy
> virtio-mem: Fail if a memory backend with "prealloc=on" is specified
> virtio-mem: Migrate immutable properties early
> virtio-mem: Proper support for preallocation with migration
>
> hw/core/machine.c | 4 +-
> hw/virtio/virtio-mem.c | 144 ++++++++++++++++++++++++++++++++-
> include/hw/virtio/virtio-mem.h | 8 ++
> include/migration/misc.h | 4 +-
> include/migration/vmstate.h | 28 ++++++-
> migration/migration.c | 9 +++
> migration/migration.h | 4 +
> migration/ram.c | 8 +-
> migration/savevm.c | 105 +++++++++++++-----------
> 9 files changed, 255 insertions(+), 59 deletions(-)
>
> --
> 2.39.0