From 76634bc0645e5c0bb4e6adb9aa84097f5abeb071 Mon Sep 17 00:00:00 2001 From: Kevin Wolf Date: Wed, 24 Feb 2010 12:20:14 -0300 Subject: [PATCH 1/4] qcow2: Factor next_refcount_table_size out RH-Author: Kevin Wolf Message-id: <1267014016-12519-2-git-send-email-kwolf@redhat.com> Patchwork-id: 7258 O-Subject: [RHEL-6 KVM PATCH 1/3] qcow2: Factor next_refcount_table_size out Bugzilla: 567940 RH-Acked-by: Juan Quintela RH-Acked-by: Gleb Natapov RH-Acked-by: Christoph Hellwig Bugzilla: 567940 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 Signed-off-by: Anthony Liguori Signed-off-by: Kevin Wolf --- block/qcow2-refcount.c | 30 +++++++++++++++++++----------- 1 files changed, 19 insertions(+), 11 deletions(-) Signed-off-by: Eduardo Habkost --- block/qcow2-refcount.c | 30 +++++++++++++++++++----------- 1 files changed, 19 insertions(+), 11 deletions(-) diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c index c2a5c04..5dde80a 100644 --- a/block/qcow2-refcount.c +++ b/block/qcow2-refcount.c @@ -123,6 +123,24 @@ static int get_refcount(BlockDriverState *bs, int64_t cluster_index) return be16_to_cpu(s->refcount_block_cache[block_index]); } +/* + * 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; @@ -136,17 +154,7 @@ 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, -- 1.6.3.rc4.29.g8146