[v2,07/13] migration/ram: Discard RAM when growing RAM blocks after ram_postcopy_incoming_init()
diff mbox series

Message ID 20200221164204.105570-8-david@redhat.com
State New
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Series
  • migrate/ram: Fix resizing RAM blocks while migrating
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Commit Message

David Hildenbrand Feb. 21, 2020, 4:41 p.m. UTC
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
3. Guest started, postcopy running
- Pagefaults get resolved, pages get placed

Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
Cc: Juan Quintela <quintela@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
 migration/ram.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

Comments

Peter Xu Feb. 24, 2020, 10:28 p.m. UTC | #1
On Fri, Feb 21, 2020 at 05:41:58PM +0100, David Hildenbrand wrote:
> 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
> 3. Guest started, postcopy running
> - Pagefaults get resolved, pages get placed
> 
> Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> Cc: Juan Quintela <quintela@redhat.com>
> Cc: Peter Xu <peterx@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Peter Xu <peterx@redhat.com>

Patch
diff mbox series

diff --git a/migration/ram.c b/migration/ram.c
index 39c7d1c4a6..d5a4d69e1c 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -3714,6 +3714,7 @@  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;
     Error *err = NULL;
     RAMBlock *rb = qemu_ram_block_from_host(host, false, &offset);
@@ -3734,6 +3735,35 @@  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 = {