* Peter Xu (pet...@redhat.com) wrote:
> 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>
Reviewed-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 34e4b71052..1dc021ee53 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"
> --
> 2.26.2
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
