From d5207469f7b20a9060bad62a7b51e32fdbdd5294 Mon Sep 17 00:00:00 2001
From: Kevin Wolf <kwolf@redhat.com>
Date: Fri, 26 Mar 2010 15:08:29 -0300
Subject: [PATCH 1/3] qcow2: Factor next_refcount_table_size out

RH-Author: Kevin Wolf <kwolf@redhat.com>
Message-id: <patch-8143-clone-for-rhel55-rhel55>
Patchwork-id: 8375
O-Subject: [RHEL-5.6/5.5.z KVM PATCH 1/3] qcow2: Factor next_refcount_table_size
	out
Bugzilla: 581766
RH-Acked-by: Juan Quintela <quintela@redhat.com>
RH-Acked-by: Gleb Natapov <gleb@redhat.com>
RH-Acked-by: Christoph Hellwig <chellwig@redhat.com>

Bugzilla: 577225
Upstream commit: 05121aedc41f87e44e41e9cef55f2e49ce7ba94e

When the refcount table grows, it doesn't only grow by one entry but reserves
some space for future refcount blocks. The algorithm to calculate the number of
entries stays the same with the fixes, so factor it out before replacing the
rest.

As Juan suggested take the opportunity to simplify the code a bit.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 qemu/block-qcow2.c |   30 +++++++++++++++++++-----------
 1 files changed, 19 insertions(+), 11 deletions(-)

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
---
 qemu/block-qcow2.c |   30 +++++++++++++++++++-----------
 1 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/qemu/block-qcow2.c b/qemu/block-qcow2.c
index 6d7c89e..fa45bf4 100644
--- a/qemu/block-qcow2.c
+++ b/qemu/block-qcow2.c
@@ -2674,6 +2674,24 @@ static void free_clusters(BlockDriverState *bs,
     }
 }
 
+/*
+ * Rounds the refcount table size up to avoid growing the table for each single
+ * refcount block that is allocated.
+ */
+static unsigned int next_refcount_table_size(BDRVQcowState *s,
+    unsigned int min_size)
+{
+    unsigned int min_clusters = (min_size >> (s->cluster_bits - 3)) + 1;
+    unsigned int refcount_table_clusters =
+        MAX(1, s->refcount_table_size >> (s->cluster_bits - 3));
+
+    while (min_clusters > refcount_table_clusters) {
+        refcount_table_clusters = (refcount_table_clusters * 3 + 1) / 2;
+    }
+
+    return refcount_table_clusters << (s->cluster_bits - 3);
+}
+
 static int grow_refcount_table(BlockDriverState *bs, int min_size)
 {
     BDRVQcowState *s = bs->opaque;
@@ -2687,17 +2705,7 @@ static int grow_refcount_table(BlockDriverState *bs, int min_size)
     if (min_size <= s->refcount_table_size)
         return 0;
     /* compute new table size */
-    refcount_table_clusters = s->refcount_table_size >> (s->cluster_bits - 3);
-    for(;;) {
-        if (refcount_table_clusters == 0) {
-            refcount_table_clusters = 1;
-        } else {
-            refcount_table_clusters = (refcount_table_clusters * 3 + 1) / 2;
-        }
-        new_table_size = refcount_table_clusters << (s->cluster_bits - 3);
-        if (min_size <= new_table_size)
-            break;
-    }
+    new_table_size = next_refcount_table_size(s, min_size);
 #ifdef DEBUG_ALLOC2
     printf("grow_refcount_table from %d to %d\n",
            s->refcount_table_size,
-- 
1.7.0.3