[PATCH 9/9] kvm tools, qcow: Flush only dirty L2 tables

Pekka Enberg
2011-07-09T13:03:04Z

This patch improves qcow_l2_cache_write() to only flush dirty L2 tables.

Cc: Asias He <asias.hejun@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Prasad Joshi <prasadjoshi124@gmail.com>
Cc: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
---
tools/kvm/disk/qcow.c | 11 ++++++++++-
tools/kvm/include/kvm/qcow.h | 1 +
2 files changed, 11 insertions(+), 1 deletions(-)

diff --git a/tools/kvm/disk/qcow.c b/tools/kvm/disk/qcow.c
index b71762f..13c8bea 100644
--- a/tools/kvm/disk/qcow.c
+++ b/tools/kvm/disk/qcow.c
@@ -93,9 +93,17 @@ static int qcow_l2_cache_write(struct qcow *q, struct qcow_l2_table *c)
struct qcow_header *header = q->header;
u64 size;

+ if (!c->dirty)
+ return 0;
+
size = 1 << header->l2_bits;

- return pwrite_in_full(q->fd, c->table, size * sizeof(u64), c->offset);
+ if (pwrite_in_full(q->fd, c->table, size * sizeof(u64), c->offset) < 0)
+ return -1;
+
+ c->dirty = 0;
+
+ return 0;
}

static int cache_table(struct qcow *q, struct qcow_l2_table *c)
@@ -447,6 +455,7 @@ static ssize_t qcow_write_cluster(struct qcow *q, u64 offset, void *buf, u32 src
if (!clust_start) {
clust_start = ALIGN(f_sz, clust_sz);
l2t->table[l2t_idx] = cpu_to_be64(clust_start);
+ l2t->dirty = 1;
}

mutex_unlock(&q->mutex);
diff --git a/tools/kvm/include/kvm/qcow.h b/tools/kvm/include/kvm/qcow.h
index d44c64a..650d3c2 100644
--- a/tools/kvm/include/kvm/qcow.h
+++ b/tools/kvm/include/kvm/qcow.h
@@ -27,6 +27,7 @@ struct qcow_l2_table {
u64 offset;
struct rb_node node;
struct list_head list;
+ u8 dirty;
u64 table[];
};

--
1.7.0.4