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block: split write_zeroes always 

We should split requests even if they are less than write_zeroes_alignment.
For example we can have the following request:
  offset 62k
  size   4k
  write_zeroes_alignment 64k
The original code sent 1 request covering 2 qcow2 clusters, and resulted
in both clusters being allocated. But by splitting the request, we can
cater to the case where one of the two clusters can be zeroed as a
whole, for only 1 cluster allocated after the operation.

Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Eric Blake <eblake@redhat.com>
CC: Kevin Wolf <kwolf@redhat.com>
Message-Id: <1463476543-3087-2-git-send-email-den@openvz.org>

[eblake: Avoid exceeding nb_sectors, hoist alignment checks out of
loop, and update testsuite to show that patch works]

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Denis V. Lunev 2016-05-25 21:48:45 -06:00 committed by Kevin Wolf
parent 6ed5546fa7
commit 443668ca40
2 changed files with 29 additions and 19 deletions
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30
block/io.c
View File

@ -1118,28 +1118,32 @@ static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
struct iovec iov = {0};
int ret = 0;
bool need_flush = false;
int head = 0;
int tail = 0;
int max_write_zeroes = MIN_NON_ZERO(bs->bl.max_write_zeroes,
BDRV_REQUEST_MAX_SECTORS);
if (bs->bl.write_zeroes_alignment) {
assert(is_power_of_2(bs->bl.write_zeroes_alignment));
head = sector_num & (bs->bl.write_zeroes_alignment - 1);
tail = (sector_num + nb_sectors) & (bs->bl.write_zeroes_alignment - 1);
max_write_zeroes &= ~(bs->bl.write_zeroes_alignment - 1);
}
while (nb_sectors > 0 && !ret) {
int num = nb_sectors;
/* Align request. Block drivers can expect the "bulk" of the request
* to be aligned.
* to be aligned, and that unaligned requests do not cross cluster
* boundaries.
*/
if (bs->bl.write_zeroes_alignment
&& num > bs->bl.write_zeroes_alignment) {
if (sector_num % bs->bl.write_zeroes_alignment != 0) {
/* Make a small request up to the first aligned sector. */
num = bs->bl.write_zeroes_alignment;
num -= sector_num % bs->bl.write_zeroes_alignment;
} else if ((sector_num + num) % bs->bl.write_zeroes_alignment != 0) {
/* Shorten the request to the last aligned sector. num cannot
* underflow because num > bs->bl.write_zeroes_alignment.
*/
num -= (sector_num + num) % bs->bl.write_zeroes_alignment;
}
if (head) {
/* Make a small request up to the first aligned sector. */
num = MIN(nb_sectors, bs->bl.write_zeroes_alignment - head);
head = 0;
} else if (tail && num > bs->bl.write_zeroes_alignment) {
/* Shorten the request to the last aligned sector. */
num -= tail;
}
/* limit request size */

18
tests/qemu-iotests/154.out
View File

@ -106,11 +106,14 @@ read 1024/1024 bytes at offset 67584
read 5120/5120 bytes at offset 68608
5 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
[{ "start": 0, "length": 32768, "depth": 1, "zero": true, "data": false},
{ "start": 32768, "length": 8192, "depth": 0, "zero": false, "data": true, "offset": 20480},
{ "start": 32768, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 20480},
{ "start": 36864, "length": 4096, "depth": 0, "zero": true, "data": false},
{ "start": 40960, "length": 8192, "depth": 1, "zero": true, "data": false},
{ "start": 49152, "length": 8192, "depth": 0, "zero": false, "data": true, "offset": 28672},
{ "start": 49152, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 24576},
{ "start": 53248, "length": 4096, "depth": 0, "zero": true, "data": false},
{ "start": 57344, "length": 8192, "depth": 1, "zero": true, "data": false},
{ "start": 65536, "length": 8192, "depth": 0, "zero": false, "data": true, "offset": 36864},
{ "start": 65536, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 28672},
{ "start": 69632, "length": 4096, "depth": 0, "zero": true, "data": false},
{ "start": 73728, "length": 134144000, "depth": 1, "zero": true, "data": false}]
== spanning two clusters, non-zero after request ==
@ -145,11 +148,14 @@ read 7168/7168 bytes at offset 65536
read 1024/1024 bytes at offset 72704
1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
[{ "start": 0, "length": 32768, "depth": 1, "zero": true, "data": false},
{ "start": 32768, "length": 8192, "depth": 0, "zero": false, "data": true, "offset": 20480},
{ "start": 32768, "length": 4096, "depth": 0, "zero": true, "data": false},
{ "start": 36864, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 20480},
{ "start": 40960, "length": 8192, "depth": 1, "zero": true, "data": false},
{ "start": 49152, "length": 8192, "depth": 0, "zero": false, "data": true, "offset": 28672},
{ "start": 49152, "length": 4096, "depth": 0, "zero": true, "data": false},
{ "start": 53248, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 24576},
{ "start": 57344, "length": 8192, "depth": 1, "zero": true, "data": false},
{ "start": 65536, "length": 8192, "depth": 0, "zero": false, "data": true, "offset": 36864},
{ "start": 65536, "length": 4096, "depth": 0, "zero": true, "data": false},
{ "start": 69632, "length": 4096, "depth": 0, "zero": false, "data": true, "offset": 28672},
{ "start": 73728, "length": 134144000, "depth": 1, "zero": true, "data": false}]
== spanning two clusters, partially overwriting backing file ==