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Alberto Garcia b70d08205b qcow2: Fix the calculation of the maximum L2 cache size 
The size of the qcow2 L2 cache defaults to 32 MB, which can be easily
larger than the maximum amount of L2 metadata that the image can have.
For example: with 64 KB clusters the user would need a qcow2 image
with a virtual size of 256 GB in order to have 32 MB of L2 metadata.

Because of that, since commit b749562d98
we forbid the L2 cache to become larger than the maximum amount of L2
metadata for the image, calculated using this formula:

    uint64_t max_l2_cache = virtual_disk_size / (s->cluster_size / 8);

The problem with this formula is that the result should be rounded up
to the cluster size because an L2 table on disk always takes one full
cluster.

For example, a 1280 MB qcow2 image with 64 KB clusters needs exactly
160 KB of L2 metadata, but we need 192 KB on disk (3 clusters) even if
the last 32 KB of those are not going to be used.

However QEMU rounds the numbers down and only creates 2 cache tables
(128 KB), which is not enough for the image.

A quick test doing 4KB random writes on a 1280 MB image gives me
around 500 IOPS, while with the correct cache size I get 16K IOPS.

Cc: qemu-stable@nongnu.org
Signed-off-by: Alberto Garcia <berto@igalia.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
 		2019-09-10 08:58:43 +02:00
..
Makefile.objs ssh: switch from libssh2 to libssh 2019-06-24 16:01:04 +02:00
accounting.c block/accounting: introduce latency histogram 2018-03-19 14:58:37 -05:00
backup.c block: define .*_part io handlers in BlockDriver 2019-08-27 14:58:42 +01:00
blkdebug.c blkdebug: Inject errors on .bdrv_co_block_status() 2019-06-14 14:16:57 +02:00
blklogwrites.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
blkreplay.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
blkverify.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
block-backend.c Block layer patches: 2019-08-16 16:43:46 +01:00
bochs.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
cloop.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
commit.c block-backend: Queue requests while drained 2019-08-16 10:25:16 +02:00
copy-on-read.c block/copy-on-read: Fix permissions for inactive node 2019-07-30 12:25:43 +02:00
create.c Include qemu/main-loop.h less 2019-08-16 13:31:52 +02:00
crypto.c LUKS: support preallocation 2019-08-19 17:13:26 +02:00
crypto.h Clean up ill-advised or unusual header guards 2019-05-13 08:58:55 +02:00
curl.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
dirty-bitmap.c qapi: implement block-dirty-bitmap-remove transaction action 2019-08-16 16:28:03 -04:00
dmg-bz2.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
dmg-lzfse.c block: adding lzfse decompressing support as a module. 2018-12-14 11:52:40 +01:00
dmg.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
dmg.h Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
file-posix.c block: workaround for unaligned byte range in fallocate() 2019-09-05 16:01:31 -05:00
file-win32.c block: Implement .bdrv_has_zero_init_truncate() 2019-08-19 17:13:26 +02:00
gluster.c block: Implement .bdrv_has_zero_init_truncate() 2019-08-19 17:13:26 +02:00
io.c block: workaround for unaligned byte range in fallocate() 2019-09-05 16:01:31 -05:00
iscsi-opts.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
iscsi.c iscsi: base all handling of check condition on scsi_sense_to_errno 2019-07-15 11:20:42 +02:00
linux-aio.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
mirror.c mirror: Fix bdrv_has_zero_init() use 2019-08-19 17:13:26 +02:00
nbd.c nbd: Implement client use of NBD FAST_ZERO 2019-09-05 16:03:26 -05:00
nfs.c block: Implement .bdrv_has_zero_init_truncate() 2019-08-19 17:13:26 +02:00
null.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
nvme.c Include qemu/main-loop.h less 2019-08-16 13:31:52 +02:00
parallels.c block: Use bdrv_has_zero_init_truncate() 2019-08-19 17:13:26 +02:00
parallels.h Clean up includes 2018-02-09 05:05:11 +01:00
qapi.c qapi: add dirty-bitmaps to query-named-block-nodes result 2019-08-16 18:29:43 -04:00
qcow.c block/qcow: Improve error when opening qcow2 files as qcow 2019-07-08 16:00:26 +02:00
qcow2-bitmap.c qcow2-bitmap: initialize bitmap directory alignment 2019-05-28 20:30:55 +02:00
qcow2-cache.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
qcow2-cluster.c block/qcow2: implement .bdrv_co_pwritev(_compressed)_part 2019-08-27 14:58:42 +01:00
qcow2-refcount.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
qcow2-snapshot.c qcow2.h: add missing include 2019-05-28 20:30:55 +02:00
qcow2-threads.c qcow2: do encryption in threads 2019-05-28 20:30:55 +02:00
qcow2.c qcow2: Fix the calculation of the maximum L2 cache size 2019-09-10 08:58:43 +02:00
qcow2.h block/qcow2: implement .bdrv_co_pwritev(_compressed)_part 2019-08-27 14:58:42 +01:00
qed-check.c block/qed: add missed coroutine_fn markers 2019-04-30 15:29:00 +02:00
qed-cluster.c qed: protect table cache with CoMutex 2017-07-17 11:34:11 +08:00
qed-l2-cache.c qed: protect table cache with CoMutex 2017-07-17 11:34:11 +08:00
qed-table.c block/qed: add missed coroutine_fn markers 2019-04-30 15:29:00 +02:00
qed.c block: Implement .bdrv_has_zero_init_truncate() 2019-08-19 17:13:26 +02:00
qed.h block/qed: add missed coroutine_fn markers 2019-04-30 15:29:00 +02:00
quorum.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
raw-format.c block: Implement .bdrv_has_zero_init_truncate() 2019-08-19 17:13:26 +02:00
rbd.c block: Implement .bdrv_has_zero_init_truncate() 2019-08-19 17:13:26 +02:00
replication.c block/backup: Add mirror sync mode 'bitmap' 2019-08-16 16:28:02 -04:00
sheepdog.c block: Implement .bdrv_has_zero_init_truncate() 2019-08-19 17:13:26 +02:00
snapshot.c block/snapshot: remove bdrv_snapshot_delete_by_id_or_name 2019-02-25 15:03:18 +01:00
ssh.c block: Implement .bdrv_has_zero_init_truncate() 2019-08-19 17:13:26 +02:00
stream.c block/stream: use BDRV_REQ_PREFETCH 2019-08-15 13:22:13 -05:00
throttle-groups.c Include qemu/main-loop.h less 2019-08-16 13:31:52 +02:00
throttle.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
trace-events block/backup: teach TOP to never copy unallocated regions 2019-08-16 16:28:03 -04:00
vdi.c vdi: Make block_status recurse for fixed images 2019-08-19 17:13:26 +02:00
vhdx-endian.c Include qemu-common.h exactly where needed 2019-06-12 13:20:20 +02:00
vhdx-log.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
vhdx.c vhdx: Fix .bdrv_has_zero_init() 2019-08-19 17:13:26 +02:00
vhdx.h block/vhdx: Use IEC binary prefixes for size constants 2019-04-30 15:29:00 +02:00
vmdk.c vmdk: Reject invalid compressed writes 2019-09-03 14:55:35 +02:00
vpc.c vpc: Do not return RAW from block_status 2019-08-19 17:13:26 +02:00
vvfat.c qemu-common: Move qemu_isalnum() etc. to qemu/ctype.h 2019-06-11 20:22:09 +02:00
vxhs.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
win32-aio.c Include qemu/module.h where needed, drop it from qemu-common.h 2019-06-12 13:18:33 +02:00
write-threshold.c qapi: Drop qapi_event_send_FOO()'s Error ** argument 2018-08-28 18:21:38 +02:00