If all the bits in a dirty bitmap cluster are ones, the cluster shouldn't
be written. Instead the corresponding L1 entry should be set to 1.

Check if all bits in a memory region are ones and set 1 to L1 entries
corresponding clusters filled with ones.

Signed-off-by: Alexander Ivanov <alexander.ivanov@virtuozzo.com>
---
 block/parallels-ext.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/block/parallels-ext.c b/block/parallels-ext.c
index a0de4f1b07..ebda6b0a01 100644
--- a/block/parallels-ext.c
+++ b/block/parallels-ext.c
@@ -354,7 +354,7 @@ static void parallels_save_bitmap(BlockDriverState *bs, BdrvDirtyBitmap *bitmap,
     offset = 0;
     while ((offset = bdrv_dirty_bitmap_next_dirty(bitmap, offset, bm_size)) >= 0) {
         uint64_t idx = offset / limit;
-        int64_t cluster_off, end, write_size;
+        int64_t cluster_off, end, write_size, first_zero;
 
         offset = QEMU_ALIGN_DOWN(offset, limit);
         end = MIN(bm_size, offset + limit);
@@ -367,6 +367,16 @@ static void parallels_save_bitmap(BlockDriverState *bs, BdrvDirtyBitmap *bitmap,
             memset(bm_buf + write_size, 0, s->cluster_size - write_size);
         }
 
+        first_zero = bdrv_dirty_bitmap_next_zero(bitmap, offset, bm_size);
+        if (first_zero < 0) {
+            goto end;
+        }
+        if (first_zero - offset >= s->cluster_size) {
+            l1_table[idx] = 1;
+            offset = end;
+            continue;
+        }
+
         cluster_off = parallels_allocate_host_clusters(bs, &alloc_size);
         if (cluster_off <= 0) {
             goto end;
-- 
2.34.1