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[Qemu-devel] [PULL 02/33] qcow2: Discard VM state in active L1 after cre
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] [PULL 02/33] qcow2: Discard VM state in active L1 after creating snapshot |
Date: |
Fri, 13 Sep 2013 13:50:32 +0200 |
During savevm, the VM state is written to the active L1 of the image and
then a snapshot is taken. After that, the VM state isn't needed any more
in the active L1 and should be discarded. This is implemented by this
patch.
The impact of not discarding the VM state is that a snapshot can never
become smaller than any previous snapshot (because it would be padded
with old VM state), and more importantly that future savevm operations
cause unnecessary COWs (with associated flushes), which makes subsequent
snapshots much slower.
Signed-off-by: Kevin Wolf <address@hidden>
Reviewed-by: Max Reitz <address@hidden>
---
block/qcow2-snapshot.c | 7 +++++++
block/qcow2.c | 5 -----
block/qcow2.h | 5 +++++
3 files changed, 12 insertions(+), 5 deletions(-)
diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index e7e6013..ffead08 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -416,6 +416,13 @@ int qcow2_snapshot_create(BlockDriverState *bs,
QEMUSnapshotInfo *sn_info)
g_free(old_snapshot_list);
+ /* The VM state isn't needed any more in the active L1 table; in fact, it
+ * hurts by causing expensive COW for the next snapshot. */
+ qcow2_discard_clusters(bs, qcow2_vm_state_offset(s),
+ align_offset(sn->vm_state_size, s->cluster_size)
+ >> BDRV_SECTOR_BITS,
+ QCOW2_DISCARD_NEVER);
+
#ifdef DEBUG_ALLOC
{
BdrvCheckResult result = {0};
diff --git a/block/qcow2.c b/block/qcow2.c
index 147822e..c9e266e 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1757,11 +1757,6 @@ static coroutine_fn int
qcow2_co_flush_to_os(BlockDriverState *bs)
return 0;
}
-static int64_t qcow2_vm_state_offset(BDRVQcowState *s)
-{
- return (int64_t)s->l1_vm_state_index << (s->cluster_bits + s->l2_bits);
-}
-
static int qcow2_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
{
BDRVQcowState *s = bs->opaque;
diff --git a/block/qcow2.h b/block/qcow2.h
index 9c33b98..49eed82 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -361,6 +361,11 @@ static inline int64_t align_offset(int64_t offset, int n)
return offset;
}
+static inline int64_t qcow2_vm_state_offset(BDRVQcowState *s)
+{
+ return (int64_t)s->l1_vm_state_index << (s->cluster_bits + s->l2_bits);
+}
+
static inline int qcow2_get_cluster_type(uint64_t l2_entry)
{
if (l2_entry & QCOW_OFLAG_COMPRESSED) {
--
1.8.1.4
- [Qemu-devel] [PULL 00/33] Block patches, Kevin Wolf, 2013/09/13
- [Qemu-devel] [PULL 03/33] raw-win32.c: Fix incorrect handling behaviour of small block files, Kevin Wolf, 2013/09/13
- [Qemu-devel] [PULL 04/33] block: Image file option amendment, Kevin Wolf, 2013/09/13
- [Qemu-devel] [PULL 06/33] qcow2-cluster: Expand zero clusters, Kevin Wolf, 2013/09/13
- [Qemu-devel] [PULL 05/33] qcow2-cache: Empty cache, Kevin Wolf, 2013/09/13
- [Qemu-devel] [PULL 07/33] qcow2: Save refcount order in BDRVQcowState, Kevin Wolf, 2013/09/13
- [Qemu-devel] [PULL 01/33] qcow2: Pass discard type to qcow2_discard_clusters(), Kevin Wolf, 2013/09/13
- [Qemu-devel] [PULL 02/33] qcow2: Discard VM state in active L1 after creating snapshot,
Kevin Wolf <=
- [Qemu-devel] [PULL 11/33] qemu-iotests: add infrastructure of fd passing via SCM, Kevin Wolf, 2013/09/13
- [Qemu-devel] [PULL 10/33] qemu-iotests: add unix socket help program, Kevin Wolf, 2013/09/13
- [Qemu-devel] [PULL 09/33] qemu-iotest: qcow2 image option amendment, Kevin Wolf, 2013/09/13
- [Qemu-devel] [PULL 08/33] qcow2: Implement bdrv_amend_options, Kevin Wolf, 2013/09/13
- [Qemu-devel] [PULL 12/33] qemu-iotests: add tests for runtime fd passing via SCM rights, Kevin Wolf, 2013/09/13
- [Qemu-devel] [PULL 13/33] qemu-iotests: New test case in 061, Kevin Wolf, 2013/09/13
- [Qemu-devel] [PULL 15/33] snapshot: distinguish id and name in snapshot delete, Kevin Wolf, 2013/09/13
- [Qemu-devel] [PULL 14/33] snapshot: new function bdrv_snapshot_find_by_id_and_name(), Kevin Wolf, 2013/09/13