migration/multifd: Add new migration option zero-page-detection.

This new parameter controls where the zero page checking is running.
1. If this parameter is set to 'legacy', zero page checking is
done in the migration main thread.
2. If this parameter is set to 'none', zero page checking is disabled.

Signed-off-by: Hao Xiang <hao.xiang@bytedance.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Link: https://lore.kernel.org/r/20240311180015.3359271-4-hao.xiang@linux.dev
Signed-off-by: Peter Xu <peterx@redhat.com>

4 files changed, 35 insertions, 0 deletions

diff --git a/migration/migration-hmp-cmds.c b/migration/migration-hmp-cmds.c
index 99b49df..7e96ae6 100644
--- a/migration/migration-hmp-cmds.c
+++ b/migration/migration-hmp-cmds.c
@@ -344,6 +344,11 @@ void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict)
         monitor_printf(mon, "%s: %s\n",
             MigrationParameter_str(MIGRATION_PARAMETER_MULTIFD_COMPRESSION),
             MultiFDCompression_str(params->multifd_compression));
+        assert(params->has_zero_page_detection);
+        monitor_printf(mon, "%s: %s\n",
+            MigrationParameter_str(MIGRATION_PARAMETER_ZERO_PAGE_DETECTION),
+            qapi_enum_lookup(&ZeroPageDetection_lookup,
+                params->zero_page_detection));
         monitor_printf(mon, "%s: %" PRIu64 " bytes\n",
             MigrationParameter_str(MIGRATION_PARAMETER_XBZRLE_CACHE_SIZE),
             params->xbzrle_cache_size);
@@ -634,6 +639,10 @@ void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
         p->has_multifd_zstd_level = true;
         visit_type_uint8(v, param, &p->multifd_zstd_level, &err);
         break;
+    case MIGRATION_PARAMETER_ZERO_PAGE_DETECTION:
+        p->has_zero_page_detection = true;
+        visit_type_ZeroPageDetection(v, param, &p->zero_page_detection, &err);
+        break;
     case MIGRATION_PARAMETER_XBZRLE_CACHE_SIZE:
         p->has_xbzrle_cache_size = true;
         if (!visit_type_size(v, param, &cache_size, &err)) {
diff --git a/migration/options.c b/migration/options.c
index 09178c6..8f2a3a2 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -179,6 +179,9 @@ Property migration_properties[] = {
     DEFINE_PROP_MIG_MODE("mode", MigrationState,
                       parameters.mode,
                       MIG_MODE_NORMAL),
+    DEFINE_PROP_ZERO_PAGE_DETECTION("zero-page-detection", MigrationState,
+                       parameters.zero_page_detection,
+                       ZERO_PAGE_DETECTION_LEGACY),
 
     /* Migration capabilities */
     DEFINE_PROP_MIG_CAP("x-xbzrle", MIGRATION_CAPABILITY_XBZRLE),
@@ -938,6 +941,13 @@ uint64_t migrate_xbzrle_cache_size(void)
     return s->parameters.xbzrle_cache_size;
 }
 
+ZeroPageDetection migrate_zero_page_detection(void)
+{
+    MigrationState *s = migrate_get_current();
+
+    return s->parameters.zero_page_detection;
+}
+
 /* parameter setters */
 
 void migrate_set_block_incremental(bool value)
@@ -1048,6 +1058,8 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
     params->vcpu_dirty_limit = s->parameters.vcpu_dirty_limit;
     params->has_mode = true;
     params->mode = s->parameters.mode;
+    params->has_zero_page_detection = true;
+    params->zero_page_detection = s->parameters.zero_page_detection;
 
     return params;
 }
@@ -1084,6 +1096,7 @@ void migrate_params_init(MigrationParameters *params)
     params->has_x_vcpu_dirty_limit_period = true;
     params->has_vcpu_dirty_limit = true;
     params->has_mode = true;
+    params->has_zero_page_detection = true;
 }
 
 /*
@@ -1398,6 +1411,10 @@ static void migrate_params_test_apply(MigrateSetParameters *params,
     if (params->has_mode) {
         dest->mode = params->mode;
     }
+
+    if (params->has_zero_page_detection) {
+        dest->zero_page_detection = params->zero_page_detection;
+    }
 }
 
 static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
@@ -1548,6 +1565,10 @@ static void migrate_params_apply(MigrateSetParameters *params, Error **errp)
     if (params->has_mode) {
         s->parameters.mode = params->mode;
     }
+
+    if (params->has_zero_page_detection) {
+        s->parameters.zero_page_detection = params->zero_page_detection;
+    }
 }
 
 void qmp_migrate_set_parameters(MigrateSetParameters *params, Error **errp)
diff --git a/migration/options.h b/migration/options.h
index b6b69c2..ab8199e 100644
--- a/migration/options.h
+++ b/migration/options.h
@@ -90,6 +90,7 @@ const char *migrate_tls_authz(void);
 const char *migrate_tls_creds(void);
 const char *migrate_tls_hostname(void);
 uint64_t migrate_xbzrle_cache_size(void);
+ZeroPageDetection migrate_zero_page_detection(void);
 
 /* parameters setters */
 
diff --git a/migration/ram.c b/migration/ram.c
index dec2e73..260529f 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1140,6 +1140,10 @@ static int save_zero_page(RAMState *rs, PageSearchStatus *pss,
     QEMUFile *file = pss->pss_channel;
     int len = 0;
 
+    if (migrate_zero_page_detection() == ZERO_PAGE_DETECTION_NONE) {
+        return 0;
+    }
+
     if (!buffer_is_zero(p, TARGET_PAGE_SIZE)) {
         return 0;
     }