qcow2: use one single memory block for the L2/refcount cache tables

The qcow2 L2/refcount cache contains one separate table for each cache
entry. Doing one allocation per table adds unnecessary overhead and it
also requires us to store the address of each table separately.

Since the size of the cache is constant during its lifetime, it's
better to have an array that contains all the tables using one single
allocation.

In my tests measuring freshly created caches with sizes 128MB (L2) and
32MB (refcount) this uses around 10MB of RAM less.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 83467c3..0707f94 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -424,7 +424,7 @@ static int alloc_refcount_block(BlockDriverState *bs,
 
     /* Now the new refcount block needs to be written to disk */
     BLKDBG_EVENT(bs->file, BLKDBG_REFBLOCK_ALLOC_WRITE);
-    qcow2_cache_entry_mark_dirty(s->refcount_block_cache, *refcount_block);
+    qcow2_cache_entry_mark_dirty(bs, s->refcount_block_cache, *refcount_block);
     ret = qcow2_cache_flush(bs, s->refcount_block_cache);
     if (ret < 0) {
         goto fail_block;
@@ -737,7 +737,8 @@ static int QEMU_WARN_UNUSED_RESULT update_refcount(BlockDriverState *bs,
         }
         old_table_index = table_index;
 
-        qcow2_cache_entry_mark_dirty(s->refcount_block_cache, refcount_block);
+        qcow2_cache_entry_mark_dirty(bs, s->refcount_block_cache,
+                                     refcount_block);
 
         /* we can update the count and save it */
         block_index = cluster_index & (s->refcount_block_size - 1);
@@ -1182,7 +1183,8 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
                             s->refcount_block_cache);
                     }
                     l2_table[j] = cpu_to_be64(offset);
-                    qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_table);
+                    qcow2_cache_entry_mark_dirty(bs, s->l2_table_cache,
+                                                 l2_table);
                 }
             }