[Qemu-devel] [PATCH QEMU 5/5] migration: Add the interface for cache drop control

[Liang Li <liang.z.li@intel.com>]

Whether drop the cache and drop what kind of cache depend on the
user, add the related qmp and hmp interface to query and set the
cache control value.

Signed-off-by: Liang Li <liang.z.li@intel.com>
---
 hmp.c                         |  8 ++++++++
 include/migration/migration.h |  1 +
 migration/migration.c         | 31 ++++++++++++++++++++++++++++++-
 migration/ram.c               | 10 ++--------
 qapi-schema.json              | 25 ++++++++++++++++++++++---
 5 files changed, 63 insertions(+), 12 deletions(-)

diff --git a/hmp.c b/hmp.c
index d510236..17f418e 100644
--- a/hmp.c
+++ b/hmp.c
@@ -286,6 +286,9 @@ void hmp_info_migrate_parameters(Monitor *mon, const QDict *qdict)
         monitor_printf(mon, " %s: %" PRId64,
             MigrationParameter_lookup[MIGRATION_PARAMETER_X_CPU_THROTTLE_INCREMENT],
             params->x_cpu_throttle_increment);
+        monitor_printf(mon, " %s: %" PRId64,
+            MigrationParameter_lookup[MIGRATION_PARAMETER_X_DROP_CACHE],
+            params->x_drop_cache);
         monitor_printf(mon, "\n");
     }
 
@@ -1242,6 +1245,7 @@ void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
     bool has_decompress_threads = false;
     bool has_x_cpu_throttle_initial = false;
     bool has_x_cpu_throttle_increment = false;
+    bool has_x_drop_cache = false;
     int i;
 
     for (i = 0; i < MIGRATION_PARAMETER__MAX; i++) {
@@ -1262,12 +1266,16 @@ void hmp_migrate_set_parameter(Monitor *mon, const QDict *qdict)
             case MIGRATION_PARAMETER_X_CPU_THROTTLE_INCREMENT:
                 has_x_cpu_throttle_increment = true;
                 break;
+            case MIGRATION_PARAMETER_X_DROP_CACHE:
+                has_x_drop_cache = true;
+                break;
             }
             qmp_migrate_set_parameters(has_compress_level, value,
                                        has_compress_threads, value,
                                        has_decompress_threads, value,
                                        has_x_cpu_throttle_initial, value,
                                        has_x_cpu_throttle_increment, value,
+                                       has_x_drop_cache, value,
                                        &err);
             break;
         }
diff --git a/include/migration/migration.h b/include/migration/migration.h
index ac2c12c..873e3bc 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -283,6 +283,7 @@ bool migrate_use_compression(void);
 int migrate_compress_level(void);
 int migrate_compress_threads(void);
 int migrate_decompress_threads(void);
+int migrate_drop_cache(void);
 bool migrate_use_events(void);
 
 /* Sending on the return path - generic and then for each message type */
diff --git a/migration/migration.c b/migration/migration.c
index 991313a..ecd07b8 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -52,6 +52,13 @@
 /* Define default autoconverge cpu throttle migration parameters */
 #define DEFAULT_MIGRATE_X_CPU_THROTTLE_INITIAL 20
 #define DEFAULT_MIGRATE_X_CPU_THROTTLE_INCREMENT 10
+/* Default cache drop control
+ * 0: no drop
+ * 1: drop clean page cache
+ * 2: drop slab cache
+ * 3: drop both clean and slab cache
+ */
+#define DEFAULT_MIGRATE_X_DROP_CACHE 0
 
 /* Migration XBZRLE default cache size */
 #define DEFAULT_MIGRATE_CACHE_SIZE (64 * 1024 * 1024)
@@ -91,6 +98,8 @@ MigrationState *migrate_get_current(void)
                 DEFAULT_MIGRATE_X_CPU_THROTTLE_INITIAL,
         .parameters[MIGRATION_PARAMETER_X_CPU_THROTTLE_INCREMENT] =
                 DEFAULT_MIGRATE_X_CPU_THROTTLE_INCREMENT,
+        .parameters[MIGRATION_PARAMETER_X_DROP_CACHE] =
+                DEFAULT_MIGRATE_X_DROP_CACHE,
     };
 
     if (!once) {
@@ -525,6 +534,7 @@ MigrationParameters *qmp_query_migrate_parameters(Error **errp)
             s->parameters[MIGRATION_PARAMETER_X_CPU_THROTTLE_INITIAL];
     params->x_cpu_throttle_increment =
             s->parameters[MIGRATION_PARAMETER_X_CPU_THROTTLE_INCREMENT];
+    params->x_drop_cache = s->parameters[MIGRATION_PARAMETER_X_DROP_CACHE];
 
     return params;
 }
@@ -721,7 +731,9 @@ void qmp_migrate_set_parameters(bool has_compress_level,
                                 bool has_x_cpu_throttle_initial,
                                 int64_t x_cpu_throttle_initial,
                                 bool has_x_cpu_throttle_increment,
-                                int64_t x_cpu_throttle_increment, Error **errp)
+                                int64_t x_cpu_throttle_increment,
+                                bool has_x_drop_cache,
+                                int64_t x_drop_cache, Error **errp)
 {
     MigrationState *s = migrate_get_current();
 
@@ -756,6 +768,11 @@ void qmp_migrate_set_parameters(bool has_compress_level,
                    "x_cpu_throttle_increment",
                    "an integer in the range of 1 to 99");
     }
+    if (has_x_drop_cache && (x_drop_cache < 0 || x_drop_cache > 3)) {
+        error_setg(errp, QERR_INVALID_PARAMETER_VALUE,
+                   "x_drop_cache",
+                   "an integer in the range of 0 to 3");
+    }
 
     if (has_compress_level) {
         s->parameters[MIGRATION_PARAMETER_COMPRESS_LEVEL] = compress_level;
@@ -776,6 +793,9 @@ void qmp_migrate_set_parameters(bool has_compress_level,
         s->parameters[MIGRATION_PARAMETER_X_CPU_THROTTLE_INCREMENT] =
                                                     x_cpu_throttle_increment;
     }
+    if (has_x_drop_cache) {
+        s->parameters[MIGRATION_PARAMETER_X_DROP_CACHE] = x_drop_cache;
+    }
 }
 
 void qmp_migrate_start_postcopy(Error **errp)
@@ -1182,6 +1202,15 @@ int migrate_decompress_threads(void)
     return s->parameters[MIGRATION_PARAMETER_DECOMPRESS_THREADS];
 }
 
+int migrate_drop_cache(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters[MIGRATION_PARAMETER_X_DROP_CACHE];
+}
+
 bool migrate_use_events(void)
 {
     MigrationState *s;
diff --git a/migration/ram.c b/migration/ram.c
index 3944426..0d5fc97 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -229,7 +229,6 @@ static uint64_t migration_dirty_pages;
 static uint32_t last_version;
 static bool ram_bulk_stage;
 static bool ignore_freepage_rsp;
-static bool drop_page_cache;
 
 /* used by the search for pages to send */
 struct PageSearchStatus {
@@ -1520,12 +1519,7 @@ static void ram_request_free_page(unsigned long *bmap, unsigned long max_pfn)
 {
     FreePageStatus status;
 
-    /* drop_page_cache should be set by user, the related code will be
-     * added later, set it to ture temporarily.
-     */
-    drop_page_cache = true;
-
-    status = balloon_get_free_pages(bmap, max_pfn, drop_page_cache);
+    status = balloon_get_free_pages(bmap, max_pfn, migrate_drop_cache());
     switch (status) {
     case FREE_PAGE_REQ:
         ignore_freepage_rsp = false;
@@ -1546,7 +1540,7 @@ static void ram_handle_free_page(void)
     FreePageStatus status;
 
     status = balloon_get_free_pages(migration_bitmap_rcu->free_page_bmap,
-                                    get_guest_max_pfn(), drop_page_cache);
+                                    get_guest_max_pfn(), migrate_drop_cache());
     switch (status) {
     case FREE_PAGE_READY:
         rcu_read_lock();
diff --git a/qapi-schema.json b/qapi-schema.json
index 54634c4..8674d35 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -612,11 +612,21 @@
 # @x-cpu-throttle-increment: throttle percentage increase each time
 #                            auto-converge detects that migration is not making
 #                            progress. The default value is 10. (Since 2.5)
+# @x-drop-cache: drop guest's page cache during live migration, the value can
+#         be set to 0, 1, 2, 3. 1 means drop the clean page cache, 2 means
+#         drop the slab cache, 3 means to drop both clean page cache, 0 means
+#         do not drop any cache. Drop cache can speed up live migration
+#         process and reduce the network traffic, the side affect is the
+#         performance impact to the guest, 1 is the recommended value for
+#         proper balance between speed and performance. The value only takes
+#         affect when the virtio-balloon device are enabled and the guest
+#         has the related driver. The default value is 0. (Since 2.7)
 # Since: 2.4
 ##
 { 'enum': 'MigrationParameter',
   'data': ['compress-level', 'compress-threads', 'decompress-threads',
-           'x-cpu-throttle-initial', 'x-cpu-throttle-increment'] }
+           'x-cpu-throttle-initial', 'x-cpu-throttle-increment',
+           'x-drop-cache'] }
 
 #
 # @migrate-set-parameters
@@ -636,6 +646,10 @@
 # @x-cpu-throttle-increment: throttle percentage increase each time
 #                            auto-converge detects that migration is not making
 #                            progress. The default value is 10. (Since 2.5)
+#
+# @x-drop-cache: guest cache drop control, determine what kind of guest cache
+#       to drop during live migration. The default value is 0. (Since 2.7)
+#
 # Since: 2.4
 ##
 { 'command': 'migrate-set-parameters',
@@ -643,7 +657,8 @@
             '*compress-threads': 'int',
             '*decompress-threads': 'int',
             '*x-cpu-throttle-initial': 'int',
-            '*x-cpu-throttle-increment': 'int'} }
+            '*x-cpu-throttle-increment': 'int',
+            '*x-drop-cache': 'int'} }
 
 #
 # @MigrationParameters
@@ -662,6 +677,9 @@
 #                            auto-converge detects that migration is not making
 #                            progress. The default value is 10. (Since 2.5)
 #
+# @x-drop-cache: guest cache drop control, determine what kind of guest cache
+#       to drop during live migration. The default value is 0. (Since 2.7)
+#
 # Since: 2.4
 ##
 { 'struct': 'MigrationParameters',
@@ -669,7 +687,8 @@
             'compress-threads': 'int',
             'decompress-threads': 'int',
             'x-cpu-throttle-initial': 'int',
-            'x-cpu-throttle-increment': 'int'} }
+            'x-cpu-throttle-increment': 'int',
+            'x-drop-cache': 'int'} }
 ##
 # @query-migrate-parameters
 #
-- 
1.8.3.1