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migration/ram: Discard RAM when growing RAM blocks after ram_postcopy_incoming_init()

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In case we grow our RAM after ram_postcopy_incoming_init() (e.g., when
synchronizing the RAM block state with the migration source), the resized
part would not get discarded. Let's perform that when being notified
about a resize while postcopy has been advised, but is not listening
yet. With precopy, the process is as following:

1. VM created
- RAM blocks are created
2. Incomming migration started
- Postcopy is advised
- All pages in RAM blocks are discarded
3. Precopy starts
- RAM blocks are resized to match the size on the migration source.
- RAM pages from precopy stream are loaded
- Uffd handler is registered, postcopy starts listening
4. Guest started, postcopy running
- Pagefaults get resolved, pages get placed

Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20210429112708.12291-7-david@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
David Hildenbrand 2021-04-29 13:27:04 +02:00 committed by Dr. David Alan Gilbert
parent dcdc460767
commit cc61c703b6
1 changed files with 30 additions and 0 deletions
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30
migration/ram.c
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@ -4099,6 +4099,7 @@ static SaveVMHandlers savevm_ram_handlers = {
static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host,
size_t old_size, size_t new_size)
{
PostcopyState ps = postcopy_state_get();
ram_addr_t offset;
RAMBlock *rb = qemu_ram_block_from_host(host, false, &offset);
Error *err = NULL;
@ -4119,6 +4120,35 @@ static void ram_mig_ram_block_resized(RAMBlockNotifier *n, void *host,
error_free(err);
migration_cancel();
}
switch (ps) {
case POSTCOPY_INCOMING_ADVISE:
/*
* Update what ram_postcopy_incoming_init()->init_range() does at the
* time postcopy was advised. Syncing RAM blocks with the source will
* result in RAM resizes.
*/
if (old_size < new_size) {
if (ram_discard_range(rb->idstr, old_size, new_size - old_size)) {
error_report("RAM block '%s' discard of resized RAM failed",
rb->idstr);
}
}
break;
case POSTCOPY_INCOMING_NONE:
case POSTCOPY_INCOMING_RUNNING:
case POSTCOPY_INCOMING_END:
/*
* Once our guest is running, postcopy does no longer care about
* resizes. When growing, the new memory was not available on the
* source, no handler needed.
*/
break;
default:
error_report("RAM block '%s' resized during postcopy state: %d",
rb->idstr, ps);
exit(-1);
}
}
static RAMBlockNotifier ram_mig_ram_notifier = {