[Qemu-devel] [PATCH v2 3/3] migration: discard non-dirty ram pages after the start of postcopy

[Pavel Butsykin <pbutsykin@virtuozzo.com>]

After the start of postcopy migration there are some non-dirty pages which have
already been migrated. These pages are no longer needed on the source vm so that
we can free them and it doen't hurt to complete the migration.

Signed-off-by: Pavel Butsykin <pbutsykin@virtuozzo.com>
---
 include/migration/migration.h |  1 +
 migration/migration.c         |  4 ++++
 migration/ram.c               | 19 +++++++++++++++++++
 3 files changed, 24 insertions(+)

diff --git a/include/migration/migration.h b/include/migration/migration.h
index 401fbe1f77..3a5f8c469e 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -288,6 +288,7 @@ int ram_postcopy_send_discard_bitmap(MigrationState *ms);
 int ram_discard_range(MigrationIncomingState *mis, const char *block_name,
                       uint64_t start, size_t length);
 int ram_postcopy_incoming_init(MigrationIncomingState *mis);
+void ram_postcopy_migrated_memory_release(MigrationState *ms);
 
 /**
  * @migrate_add_blocker - prevent migration from proceeding
diff --git a/migration/migration.c b/migration/migration.c
index 8d5a5f8a6e..a9aa6a0f8b 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -1713,6 +1713,10 @@ static int postcopy_start(MigrationState *ms, bool *old_vm_running)
      */
     qemu_savevm_send_ping(ms->to_dst_file, 4);
 
+    if (migrate_release_ram()) {
+        ram_postcopy_migrated_memory_release(ms);
+    }
+
     ret = qemu_file_get_error(ms->to_dst_file);
     if (ret) {
         error_report("postcopy_start: Migration stream errored");
diff --git a/migration/ram.c b/migration/ram.c
index 5a43f716d1..ae1f10b145 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1562,6 +1562,25 @@ void ram_debug_dump_bitmap(unsigned long *todump, bool expected)
 
 /* **** functions for postcopy ***** */
 
+void ram_postcopy_migrated_memory_release(MigrationState *ms)
+{
+    struct RAMBlock *block;
+    unsigned long *bitmap = atomic_rcu_read(&migration_bitmap_rcu)->bmap;
+
+    QLIST_FOREACH_RCU(block, &ram_list.blocks, next) {
+        unsigned long first = block->offset >> TARGET_PAGE_BITS;
+        unsigned long range = first + (block->used_length >> TARGET_PAGE_BITS);
+        unsigned long run_start = find_next_zero_bit(bitmap, range, first);
+
+        while (run_start < range) {
+            unsigned long run_end = find_next_bit(bitmap, range, run_start + 1);
+            ram_discard_range(NULL, block->idstr, run_start << TARGET_PAGE_BITS,
+                              (run_end - run_start) << TARGET_PAGE_BITS);
+            run_start = find_next_zero_bit(bitmap, range, run_end + 1);
+        }
+    }
+}
+
 /*
  * Callback from postcopy_each_ram_send_discard for each RAMBlock
  * Note: At this point the 'unsentmap' is the processed bitmap combined
-- 
2.11.0