From: Peter Xu <pet...@redhat.com>
We synchronize the requested pages right after a postcopy recovery happens.
This helps to synchronize the prioritized pages on source so that the faulted
threads can be served faster.
Reported-by: Xiaohui Li <xiao...@redhat.com>
Signed-off-by: Peter Xu <pet...@redhat.com>
Message-Id: <20201002175336.30858-5-pet...@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
---
migration/savevm.c | 57 ++++++++++++++++++++++++++++++++++++++++++
migration/trace-events | 1 +
2 files changed, 58 insertions(+)
diff --git a/migration/savevm.c b/migration/savevm.c
index d2e141f7b1..33acbba1a4 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2011,6 +2011,49 @@ static int
loadvm_postcopy_handle_run(MigrationIncomingState *mis)
return LOADVM_QUIT;
}
+/* We must be with page_request_mutex held */
+static gboolean postcopy_sync_page_req(gpointer key, gpointer value,
+ gpointer data)
+{
+ MigrationIncomingState *mis = data;
+ void *host_addr = (void *) key;
+ ram_addr_t rb_offset;
+ RAMBlock *rb;
+ int ret;
+
+ rb = qemu_ram_block_from_host(host_addr, true, &rb_offset);
+ if (!rb) {
+ /*
+ * This should _never_ happen. However be nice for a migrating VM to
+ * not crash/assert. Post an error (note: intended to not use *_once
+ * because we do want to see all the illegal addresses; and this can
+ * never be triggered by the guest so we're safe) and move on next.
+ */
+ error_report("%s: illegal host addr %p", __func__, host_addr);
+ /* Try the next entry */
+ return FALSE;
+ }
+
+ ret = migrate_send_rp_message_req_pages(mis, rb, rb_offset);
+ if (ret) {
+ /* Please refer to above comment. */
+ error_report("%s: send rp message failed for addr %p",
+ __func__, host_addr);
+ return FALSE;
+ }
+
+ trace_postcopy_page_req_sync(host_addr);
+
+ return FALSE;
+}
+
+static void migrate_send_rp_req_pages_pending(MigrationIncomingState *mis)
+{
+ WITH_QEMU_LOCK_GUARD(&mis->page_request_mutex) {
+ g_tree_foreach(mis->page_requested, postcopy_sync_page_req, mis);
+ }
+}
+
static int loadvm_postcopy_handle_resume(MigrationIncomingState *mis)
{
if (mis->state != MIGRATION_STATUS_POSTCOPY_RECOVER) {
@@ -2033,6 +2076,20 @@ static int
loadvm_postcopy_handle_resume(MigrationIncomingState *mis)
/* Tell source that "we are ready" */
migrate_send_rp_resume_ack(mis, MIGRATION_RESUME_ACK_VALUE);
+ /*
+ * After a postcopy recovery, the source should have lost the postcopy
+ * queue, or potentially the requested pages could have been lost during
+ * the network down phase. Let's re-sync with the source VM by re-sending
+ * all the pending pages that we eagerly need, so these threads won't get
+ * blocked too long due to the recovery.
+ *
+ * Without this procedure, the faulted destination VM threads (waiting for
+ * page requests right before the postcopy is interrupted) can keep hanging
+ * until the pages are sent by the source during the background copying of
+ * pages, or another thread faulted on the same address accidentally.
+ */
+ migrate_send_rp_req_pages_pending(mis);
+
return 0;
}
diff --git a/migration/trace-events b/migration/trace-events
index e4d5eb94ca..0fbfd2da60 100644
--- a/migration/trace-events
+++ b/migration/trace-events
@@ -49,6 +49,7 @@ vmstate_save(const char *idstr, const char *vmsd_name) "%s,
%s"
vmstate_load(const char *idstr, const char *vmsd_name) "%s, %s"
postcopy_pause_incoming(void) ""
postcopy_pause_incoming_continued(void) ""
+postcopy_page_req_sync(void *host_addr) "sync page req %p"
# vmstate.c
vmstate_load_field_error(const char *field, int ret) "field \"%s\" load
failed, ret = %d"
--
2.28.0
