Re: [PATCH v5 0/8] virtio-mem: Handle preallocation with migration

[Juan Quintela]

David Hildenbrand <david@redhat.com> wrote:
> On 17.01.23 12:22, 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>
>
> @Juan, David: I can similarly take this via my tree as well.

Reviewing it.

I can get it through migration tree, thanks.

Later, Juan.