block/block-copy: refactor task creation

Instead of just relying on the comment "Called only on full-dirty
region" in block_copy_task_create() let's move initial dirty area
search directly to block_copy_task_create(). Let's also use effective
bdrv_dirty_bitmap_next_dirty_area instead of looping through all
non-dirty clusters.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20200429130847.28124-5-vsementsov@virtuozzo.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>

block/block-copy.c

@@ -32,6 +32,11 @@ typedef struct BlockCopyTask {
     CoQueue wait_queue; /* coroutines blocked on this task */
 } BlockCopyTask;
 
+static int64_t task_end(BlockCopyTask *task)
+{
+    return task->offset + task->bytes;
+}
+
 typedef struct BlockCopyState {
     /*
      * BdrvChild objects are not owned or managed by block-copy. They are
@@ -106,17 +111,29 @@ static bool coroutine_fn block_copy_wait_one(BlockCopyState *s, int64_t offset,
     return true;
 }
 
-/* Called only on full-dirty region */
+/*
+ * Search for the first dirty area in offset/bytes range and create task at
+ * the beginning of it.
+ */
 static BlockCopyTask *block_copy_task_create(BlockCopyState *s,
                                              int64_t offset, int64_t bytes)
 {
-    BlockCopyTask *task = g_new(BlockCopyTask, 1);
+    BlockCopyTask *task;
 
+    if (!bdrv_dirty_bitmap_next_dirty_area(s->copy_bitmap,
+                                           offset, offset + bytes,
+                                           s->copy_size, &offset, &bytes))
+    {
+        return NULL;
+    }
+
+    /* region is dirty, so no existent tasks possible in it */
     assert(!find_conflicting_task(s, offset, bytes));
 
     bdrv_reset_dirty_bitmap(s->copy_bitmap, offset, bytes);
     s->in_flight_bytes += bytes;
 
+    task = g_new(BlockCopyTask, 1);
     *task = (BlockCopyTask) {
         .s = s,
         .offset = offset,
@@ -466,6 +483,7 @@ static int coroutine_fn block_copy_dirty_clusters(BlockCopyState *s,
 {
     int ret = 0;
     bool found_dirty = false;
+    int64_t end = offset + bytes;
 
     /*
      * block_copy() user is responsible for keeping source and target in same
@@ -479,58 +497,52 @@ static int coroutine_fn block_copy_dirty_clusters(BlockCopyState *s,
 
     while (bytes) {
         g_autofree BlockCopyTask *task = NULL;
-        int64_t next_zero, cur_bytes, status_bytes;
+        int64_t status_bytes;
 
-        if (!bdrv_dirty_bitmap_get(s->copy_bitmap, offset)) {
-            trace_block_copy_skip(s, offset);
-            offset += s->cluster_size;
-            bytes -= s->cluster_size;
-            continue; /* already copied */
+        task = block_copy_task_create(s, offset, bytes);
+        if (!task) {
+            /* No more dirty bits in the bitmap */
+            trace_block_copy_skip_range(s, offset, bytes);
+            break;
+        }
+        if (task->offset > offset) {
+            trace_block_copy_skip_range(s, offset, task->offset - offset);
         }
 
         found_dirty = true;
 
-        cur_bytes = MIN(bytes, s->copy_size);
-
-        next_zero = bdrv_dirty_bitmap_next_zero(s->copy_bitmap, offset,
-                                                cur_bytes);
-        if (next_zero >= 0) {
-            assert(next_zero > offset); /* offset is dirty */
-            assert(next_zero < offset + cur_bytes); /* no need to do MIN() */
-            cur_bytes = next_zero - offset;
-        }
-        task = block_copy_task_create(s, offset, cur_bytes);
-
-        ret = block_copy_block_status(s, offset, cur_bytes, &status_bytes);
+        ret = block_copy_block_status(s, task->offset, task->bytes,
+                                      &status_bytes);
         assert(ret >= 0); /* never fail */
-        cur_bytes = MIN(cur_bytes, status_bytes);
-        block_copy_task_shrink(task, cur_bytes);
+        if (status_bytes < task->bytes) {
+            block_copy_task_shrink(task, status_bytes);
+        }
         if (s->skip_unallocated && !(ret & BDRV_BLOCK_ALLOCATED)) {
             block_copy_task_end(task, 0);
             progress_set_remaining(s->progress,
                                    bdrv_get_dirty_count(s->copy_bitmap) +
                                    s->in_flight_bytes);
-            trace_block_copy_skip_range(s, offset, status_bytes);
-            offset += status_bytes;
-            bytes -= status_bytes;
+            trace_block_copy_skip_range(s, task->offset, task->bytes);
+            offset = task_end(task);
+            bytes = end - offset;
             continue;
         }
 
-        trace_block_copy_process(s, offset);
+        trace_block_copy_process(s, task->offset);
 
-        co_get_from_shres(s->mem, cur_bytes);
-        ret = block_copy_do_copy(s, offset, cur_bytes, ret & BDRV_BLOCK_ZERO,
-                                 error_is_read);
-        co_put_to_shres(s->mem, cur_bytes);
+        co_get_from_shres(s->mem, task->bytes);
+        ret = block_copy_do_copy(s, task->offset, task->bytes,
+                                 ret & BDRV_BLOCK_ZERO, error_is_read);
+        co_put_to_shres(s->mem, task->bytes);
         block_copy_task_end(task, ret);
         if (ret < 0) {
             return ret;
         }
 
-        progress_work_done(s->progress, cur_bytes);
-        s->progress_bytes_callback(cur_bytes, s->progress_opaque);
-        offset += cur_bytes;
-        bytes -= cur_bytes;
+        progress_work_done(s->progress, task->bytes);
+        s->progress_bytes_callback(task->bytes, s->progress_opaque);
+        offset = task_end(task);
+        bytes = end - offset;
     }
 
     return found_dirty;