Commit 443668ca authored by Denis V. Lunev's avatar Denis V. Lunev Committed by Kevin Wolf
Browse files

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: default avatarDenis 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: default avatarEric Blake <eblake@redhat.com>
Reviewed-by: default avatarFam Zheng <famz@redhat.com>
Signed-off-by: default avatarKevin Wolf <kwolf@redhat.com>
parent 6ed5546f

block/io.c

+17 −13
Original line number Diff line number Diff line
@@ -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) {

        if (head) {

            /* 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;

            }

            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 */

tests/qemu-iotests/154.out

+12 −6
Original line number Diff line number Diff line
@@ -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 ==