qcow2: Update multiple refcounts at once

Don't write each single changed refcount block entry to the disk after it is written, but update all entries of the block and write all of them at once. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

qcow2: Update multiple refcounts at once
Don't write each single changed refcount block entry to the disk after it is written, but update all entries of the block and write all of them at once. Signed-off-by: Kevin Wolf <kwolf@redhat.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Kevin Wolf · Anthony Liguori
1 parent 44ff42de
Showing 1 changed file with 36 additions and 4 deletions
block/qcow2.c
@@ -2578,6 +2578,9 @@ static int update_refcount(BlockDriverState *bs,
 {
     BDRVQcowState *s = bs->opaque;
     int64_t start, last, cluster_offset;
+    int64_t refcount_block_offset = 0;
+    int64_t table_index = -1, old_table_index;
+    int first_index = -1, last_index = -1;
 #ifdef DEBUG_ALLOC2
     printf("update_refcount: offset=%lld size=%lld addend=%d\n",
@@ -2590,10 +2593,25 @@ static int update_refcount(BlockDriverState *bs,
     for(cluster_offset = start; cluster_offset <= last;
         cluster_offset += s->cluster_size)
     {
-        int64_t refcount_block_offset;
         int block_index, refcount;
         int64_t cluster_index = cluster_offset >> s->cluster_bits;
+        /* Only write refcount block to disk when we are done with it */
+        old_table_index = table_index;
+        table_index = cluster_index >> (s->cluster_bits - REFCOUNT_SHIFT);
+        if ((old_table_index >= 0) && (table_index != old_table_index)) {
+            size_t size = (last_index - first_index + 1) << REFCOUNT_SHIFT;
+            if (bdrv_pwrite(s->hd,
+                refcount_block_offset + (first_index << REFCOUNT_SHIFT),
+                &s->refcount_block_cache[first_index], size) != size)
+            {
+                return -EIO;
+            }
+
+            first_index = -1;
+            last_index = -1;
+        }
+
         /* Load the refcount block and allocate it if needed */
         refcount_block_offset = alloc_refcount_block(bs, cluster_index);
         if (refcount_block_offset < 0) {
@@ -2603,6 +2621,13 @@ static int update_refcount(BlockDriverState *bs,
         /* we can update the count and save it */
         block_index = cluster_index &
             ((1 << (s->cluster_bits - REFCOUNT_SHIFT)) - 1);
+        if (first_index == -1 || block_index < first_index) {
+            first_index = block_index;
+        }
+        if (block_index > last_index) {
+            last_index = block_index;
+        }
+
         refcount = be16_to_cpu(s->refcount_block_cache[block_index]);
         refcount += addend;
         if (refcount < 0 || refcount > 0xffff)
@@ -2611,12 +2636,19 @@ static int update_refcount(BlockDriverState *bs,
             s->free_cluster_index = cluster_index;
         }
         s->refcount_block_cache[block_index] = cpu_to_be16(refcount);
+    }
+
+    /* Write last changed block to disk */
+    if (refcount_block_offset != 0) {
+        size_t size = (last_index - first_index + 1) << REFCOUNT_SHIFT;
         if (bdrv_pwrite(s->hd,
-                        refcount_block_offset + (block_index << REFCOUNT_SHIFT),
-                        &s->refcount_block_cache[block_index], 2) != 2)
+            refcount_block_offset + (first_index << REFCOUNT_SHIFT),
+            &s->refcount_block_cache[first_index], size) != size)
+        {
             return -EIO;
-
+        }
     }
+
     return 0;
 }