diff --git a/block-migration.c b/block-migration.c
index 9d0b037..9ac7de6 100644
--- a/block-migration.c
+++ b/block-migration.c
@@ -23,7 +23,8 @@
 #include "sysemu/blockdev.h"
 #include <assert.h>
 
-#define BLOCK_SIZE (BDRV_SECTORS_PER_DIRTY_CHUNK << BDRV_SECTOR_BITS)
+#define BLOCK_SIZE                       (1 << 20)
+#define BDRV_SECTORS_PER_DIRTY_CHUNK     (BLOCK_SIZE >> BDRV_SECTOR_BITS)
 
 #define BLK_MIG_FLAG_DEVICE_BLOCK       0x01
 #define BLK_MIG_FLAG_EOS                0x02
@@ -254,7 +255,7 @@ static void set_dirty_tracking(int enable)
     BlkMigDevState *bmds;
 
     QSIMPLEQ_FOREACH(bmds, &block_mig_state.bmds_list, entry) {
-        bdrv_set_dirty_tracking(bmds->bs, enable);
+        bdrv_set_dirty_tracking(bmds->bs, enable ? BLOCK_SIZE : 0);
     }
 }
 
diff --git a/block.c b/block.c
index a274544..ba67c0d 100644
--- a/block.c
+++ b/block.c
@@ -2833,6 +2833,8 @@ BlockInfo *bdrv_query_info(BlockDriverState *bs)
         info->has_dirty = true;
         info->dirty = g_malloc0(sizeof(*info->dirty));
         info->dirty->count = bdrv_get_dirty_count(bs) * BDRV_SECTOR_SIZE;
+        info->dirty->granularity =
+            ((int64_t) BDRV_SECTOR_SIZE << hbitmap_granularity(bs->dirty_bitmap));
     }
 
     if (bs->drv) {
@@ -4299,16 +4301,17 @@ bool bdrv_qiov_is_aligned(BlockDriverState *bs, QEMUIOVector *qiov)
     return true;
 }
 
-void bdrv_set_dirty_tracking(BlockDriverState *bs, int enable)
+void bdrv_set_dirty_tracking(BlockDriverState *bs, int granularity)
 {
     int64_t bitmap_size;
 
-    if (enable) {
-        if (!bs->dirty_bitmap) {
-            bitmap_size = (bdrv_getlength(bs) >> BDRV_SECTOR_BITS);
-            bs->dirty_bitmap = hbitmap_alloc(bitmap_size,
-                                             BDRV_LOG_SECTORS_PER_DIRTY_CHUNK);
-        }
+    assert((granularity & (granularity - 1)) == 0);
+
+    if (granularity) {
+        granularity >>= BDRV_SECTOR_BITS;
+        assert(!bs->dirty_bitmap);
+        bitmap_size = (bdrv_getlength(bs) >> BDRV_SECTOR_BITS);
+        bs->dirty_bitmap = hbitmap_alloc(bitmap_size, ffs(granularity) - 1);
     } else {
         if (bs->dirty_bitmap) {
             hbitmap_free(bs->dirty_bitmap);
diff --git a/block/mirror.c b/block/mirror.c
index 4e36045..2d656c9 100644
--- a/block/mirror.c
+++ b/block/mirror.c
@@ -17,14 +17,8 @@
 #include "qemu/ratelimit.h"
 #include "qemu/bitmap.h"
 
-enum {
-    /*
-     * Size of data buffer for populating the image file.  This should be large
-     * enough to process multiple clusters in a single call, so that populating
-     * contiguous regions of the image is efficient.
-     */
-    BLOCK_SIZE = 512 * BDRV_SECTORS_PER_DIRTY_CHUNK, /* in bytes */
-};
+#define BLOCK_SIZE                       (1 << 20)
+#define BDRV_SECTORS_PER_DIRTY_CHUNK     (BLOCK_SIZE >> BDRV_SECTOR_BITS)
 
 #define SLICE_TIME 100000000ULL /* ns */
 
@@ -274,7 +268,7 @@ static void coroutine_fn mirror_run(void *opaque)
 immediate_exit:
     qemu_vfree(s->buf);
     g_free(s->cow_bitmap);
-    bdrv_set_dirty_tracking(bs, false);
+    bdrv_set_dirty_tracking(bs, 0);
     bdrv_iostatus_disable(s->target);
     if (s->should_complete && ret == 0) {
         if (bdrv_get_flags(s->target) != bdrv_get_flags(s->common.bs)) {
@@ -362,7 +356,7 @@ void mirror_start(BlockDriverState *bs, BlockDriverState *target,
     s->mode = mode;
     s->buf_size = BLOCK_SIZE;
 
-    bdrv_set_dirty_tracking(bs, true);
+    bdrv_set_dirty_tracking(bs, BLOCK_SIZE);
     bdrv_set_enable_write_cache(s->target, true);
     bdrv_set_on_error(s->target, on_target_error, on_target_error);
     bdrv_iostatus_enable(s->target);
diff --git a/include/block/block.h b/include/block/block.h
index 9ee9068..5c3b911 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -355,11 +355,8 @@ void bdrv_set_buffer_alignment(BlockDriverState *bs, int align);
 void *qemu_blockalign(BlockDriverState *bs, size_t size);
 bool bdrv_qiov_is_aligned(BlockDriverState *bs, QEMUIOVector *qiov);
 
-#define BDRV_SECTORS_PER_DIRTY_CHUNK     (1 << BDRV_LOG_SECTORS_PER_DIRTY_CHUNK)
-#define BDRV_LOG_SECTORS_PER_DIRTY_CHUNK 11
-
 struct HBitmapIter;
-void bdrv_set_dirty_tracking(BlockDriverState *bs, int enable);
+void bdrv_set_dirty_tracking(BlockDriverState *bs, int granularity);
 int bdrv_get_dirty(BlockDriverState *bs, int64_t sector);
 void bdrv_set_dirty(BlockDriverState *bs, int64_t cur_sector, int nr_sectors);
 void bdrv_reset_dirty(BlockDriverState *bs, int64_t cur_sector, int nr_sectors);
diff --git a/qapi-schema.json b/qapi-schema.json
index 5dfa052..75aacdd 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -667,10 +667,12 @@
 #
 # @count: number of dirty bytes according to the dirty bitmap
 #
+# @granularity: granularity of the dirty bitmap in bytes
+#
 # Since: 1.3
 ##
 { 'type': 'BlockDirtyInfo',
-  'data': {'count': 'int'} }
+  'data': {'count': 'int', 'granularity': 'int'} }
 
 ##
 # @BlockInfo:
