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authorPeter Xu <peterx@redhat.com>2020-10-21 17:27:19 -0400
committerDr. David Alan Gilbert <dgilbert@redhat.com>2020-10-26 16:15:04 +0000
commit0c26781c0937324d175b8105bc96ccce778d9760 (patch)
tree4cdf53551febac2a1b5808bed18955c72f38c808 /migration
parent8f8bfffcf1b486cee9a3bc79bb9b174682b06e22 (diff)
migration: Sync requested pages after postcopy recovery
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 <xiaohli@redhat.com> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com> Signed-off-by: Peter Xu <peterx@redhat.com> Message-Id: <20201021212721.440373-5-peterx@redhat.com> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Diffstat (limited to 'migration')
-rw-r--r--migration/savevm.c57
-rw-r--r--migration/trace-events1
2 files changed, 58 insertions, 0 deletions
diff --git a/migration/savevm.c b/migration/savevm.c
index 6ebd7e66ad..21ccba9fb3 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2010,6 +2010,49 @@ 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) {
@@ -2032,6 +2075,20 @@ 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 5f0001f808..75de5004ac 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"