On Fri, Apr 14, 2017 at 2:00 PM, Fam Zheng <f...@redhat.com> wrote:
> On Thu, 04/13 10:34, jemmy858...@gmail.com wrote:
>> From: Lidong Chen <lidongc...@tencent.com>
>>
>> BLOCK_SIZE is (1 << 20), qcow2 cluster size is 65536 by default,
>> this may cause the qcow2 file size to be bigger after migration.
>> This patch checks each cluster, using blk_pwrite_zeroes for each
>> zero cluster.
>>
>> Reviewed-by: Stefan Hajnoczi <stefa...@redhat.com>
>> Signed-off-by: Lidong Chen <lidongc...@tencent.com>
>> ---
>> v6 changelog:
>> Fix up some grammar in the comment.
>> ---
>> migration/block.c | 35 +++++++++++++++++++++++++++++++++--
>> 1 file changed, 33 insertions(+), 2 deletions(-)
>>
>> diff --git a/migration/block.c b/migration/block.c
>> index 7734ff7..41c7a55 100644
>> --- a/migration/block.c
>> +++ b/migration/block.c
>> @@ -885,6 +885,8 @@ static int block_load(QEMUFile *f, void *opaque, int
>> version_id)
>> int64_t total_sectors = 0;
>> int nr_sectors;
>> int ret;
>> + BlockDriverInfo bdi;
>> + int cluster_size;
>>
>> do {
>> addr = qemu_get_be64(f);
>> @@ -919,6 +921,15 @@ static int block_load(QEMUFile *f, void *opaque, int
>> version_id)
>> error_report_err(local_err);
>> return -EINVAL;
>> }
>> +
>> + ret = bdrv_get_info(blk_bs(blk), &bdi);
>> + if (ret == 0 && bdi.cluster_size > 0 &&
>> + bdi.cluster_size <= BLOCK_SIZE &&
>> + BLOCK_SIZE % bdi.cluster_size == 0) {
>> + cluster_size = bdi.cluster_size;
>> + } else {
>> + cluster_size = BLOCK_SIZE;
>> + }
>> }
>>
>> if (total_sectors - addr < BDRV_SECTORS_PER_DIRTY_CHUNK) {
>> @@ -932,10 +943,30 @@ static int block_load(QEMUFile *f, void *opaque, int
>> version_id)
>> nr_sectors * BDRV_SECTOR_SIZE,
>> BDRV_REQ_MAY_UNMAP);
>> } else {
>> + int i;
>> + int64_t cur_addr;
>> + uint8_t *cur_buf;
>> +
>> buf = g_malloc(BLOCK_SIZE);
>> qemu_get_buffer(f, buf, BLOCK_SIZE);
>> - ret = blk_pwrite(blk, addr * BDRV_SECTOR_SIZE, buf,
>> - nr_sectors * BDRV_SECTOR_SIZE, 0);
>> + for (i = 0; i < BLOCK_SIZE / cluster_size; i++) {
>> + cur_addr = addr * BDRV_SECTOR_SIZE + i * cluster_size;
>> + cur_buf = buf + i * cluster_size;
>> +
>> + if ((!block_mig_state.zero_blocks ||
>> + cluster_size < BLOCK_SIZE) &&
>> + buffer_is_zero(cur_buf, cluster_size)) {
>> + ret = blk_pwrite_zeroes(blk, cur_addr,
>> + cluster_size,
>> + BDRV_REQ_MAY_UNMAP);
>> + } else {
>> + ret = blk_pwrite(blk, cur_addr, cur_buf,
>> + cluster_size, 0);
>> + }
>> + if (ret < 0) {
>> + break;
>> + }
>> + }
>> g_free(buf);
>> }
>
> Sorry for asking this question so late, but, before it gets too late: did you
> evaluate the performance impact of this change under real world workload?
>
> Effectively, if no cluster is zero, this patch still splits a big write into
> small ones, which is the opposition of usual performance optimizations (i.e.
> trying to coalesce requests).
I test this patch for qcow2, the migration speed is the same before
apply this patch.
Do you know some other format which have very small cluster size?
>
> Fam
