On 1/8/20 3:40 PM, Damien Le Moal wrote:
> On 2020/01/08 16:13, Nobody wrote:
>> From: Bob Liu <bob.liu@xxxxxxxxxx>
>>
>> Motivation:
>> Now the dm-zoned device mapper target exposes a zoned block device(ZBC) as a
>> regular block device by storing metadata and buffering random writes in
>> conventional zones.
>> This way is not very flexible, there must be enough conventional zones and the
>> performance may be constrained.
>> By putting metadata(also buffering random writes) in separated device we can get
>> more flexibility and potential performance improvement e.g by storing metadata
>> in faster device like persistent memory.
>>
>> This patch try to split the metadata of dm-zoned to an extra block
>> device instead of zoned block device itself.
>> (Buffering random writes also in the todo list.)
>>
>> Patch is at the very early stage, just want to receive some feedback about
>> this extension.
>> Another option is to create an new md-zoned device with separated metadata
>> device based on md framework.
>
> For metadata only, it should not be hard at all to move to another
> conventional zone device. It will however be a little more tricky for
> conventional zones used for data since dm-zoned assumes that this random
> write space is also zoned. Moving this space to a conventional device
> requires implementing a zone emulation (fake zones) for the regular
> drive, using a zone size that matches the size of sequential zones.
>
> Beyond this, dm-zoned also needs to be changed to accept partial drives
> and the dm core code to accept mixing of regular and zoned disks (that
> is forbidden now).
>
> Another approach worth exploring is stacking dm-zoned as is on top of a
> modified dm-linear with the ability to emulate conventional zones on top
> of a regular block device (you only need report zones method
> implemented).
Looks like the only way to do this emulation is in user space tool(dm-zoned-tools).
Write metadata(which contains emulated zone information constructed by dm-zoned-tools)
into regular block device.
It's impossible to add code to every regular block device for emulating conventional zones.
Thanks,
Bob
> That is much easier to do. We actually hacked something
> like that last month to see the performance change and saw a jump from
> 56 MB/s to 250 MB/s for write intensive workloads (file creation on
> ext4). I am not so warm in this approach though as it modifies dm-linear
> and we want to keep it very lean and simple. Modifying dm-zoned to allow
> support for a device pair is a better approach I think.
>
>>
>> Signed-off-by: Bob Liu <bob.liu@xxxxxxxxxx>
>> ---
>> drivers/md/dm-zoned-metadata.c | 6 +++---
>> drivers/md/dm-zoned-target.c | 15 +++++++++++++--
>> drivers/md/dm-zoned.h | 1 +
>> 3 files changed, 17 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/md/dm-zoned-metadata.c b/drivers/md/dm-zoned-metadata.c
>> index 22b3cb0..89cd554 100644
>> --- a/drivers/md/dm-zoned-metadata.c
>> +++ b/drivers/md/dm-zoned-metadata.c
>> @@ -439,7 +439,7 @@ static struct dmz_mblock *dmz_get_mblock_slow(struct dmz_metadata *zmd,
>>
>> /* Submit read BIO */
>> bio->bi_iter.bi_sector = dmz_blk2sect(block);
>> - bio_set_dev(bio, zmd->dev->bdev);
>> + bio_set_dev(bio, zmd->dev->meta_bdev);
>> bio->bi_private = mblk;
>> bio->bi_end_io = dmz_mblock_bio_end_io;
>> bio_set_op_attrs(bio, REQ_OP_READ, REQ_META | REQ_PRIO);
>> @@ -593,7 +593,7 @@ static int dmz_write_mblock(struct dmz_metadata *zmd, struct dmz_mblock *mblk,
>> set_bit(DMZ_META_WRITING, &mblk->state);
>>
>> bio->bi_iter.bi_sector = dmz_blk2sect(block);
>> - bio_set_dev(bio, zmd->dev->bdev);
>> + bio_set_dev(bio, zmd->dev->meta_bdev);
>> bio->bi_private = mblk;
>> bio->bi_end_io = dmz_mblock_bio_end_io;
>> bio_set_op_attrs(bio, REQ_OP_WRITE, REQ_META | REQ_PRIO);
>> @@ -620,7 +620,7 @@ static int dmz_rdwr_block(struct dmz_metadata *zmd, int op, sector_t block,
>> return -ENOMEM;
>>
>> bio->bi_iter.bi_sector = dmz_blk2sect(block);
>> - bio_set_dev(bio, zmd->dev->bdev);
>> + bio_set_dev(bio, zmd->dev->meta_bdev);
>> bio_set_op_attrs(bio, op, REQ_SYNC | REQ_META | REQ_PRIO);
>> bio_add_page(bio, page, DMZ_BLOCK_SIZE, 0);
>> ret = submit_bio_wait(bio);
>> diff --git a/drivers/md/dm-zoned-target.c b/drivers/md/dm-zoned-target.c
>> index 70a1063..55c64fe 100644
>> --- a/drivers/md/dm-zoned-target.c
>> +++ b/drivers/md/dm-zoned-target.c
>> @@ -39,6 +39,7 @@ struct dm_chunk_work {
>> */
>> struct dmz_target {
>> struct dm_dev *ddev;
>> + struct dm_dev *metadata_dev;
>
> This naming would be confusing as it implies metadata only. If you also
> want to move the random write zones to a regular device, then I would
> suggest names like:
>
> ddev -> zoned_bdev (the zoned device, e.g. SMR disk)
> metadata_dev -> reg_bdev (regular block device, e.g. an SSD)
>
> The metadata+random write (fake) zones space can use the regular block
> device, and all sequential zones are assumed to be on the zoned device.
> Care must be taken to handle the case of a zoned device that has
> conventional zones: these could be used as is, not needing any reclaim,
> so potentially contributing to further optimization.
>
>>
>> unsigned long flags;
>>
>> @@ -701,6 +702,7 @@ static int dmz_get_zoned_device(struct dm_target *ti, char *path)
>> goto err;
>> }
>>
>> + dev->meta_bdev = dmz->metadata_dev->bdev;
>> dev->bdev = dmz->ddev->bdev;
>> (void)bdevname(dev->bdev, dev->name);
>>
>> @@ -761,7 +763,7 @@ static int dmz_ctr(struct dm_target *ti, unsigned int argc, char **argv)
>> int ret;
>>
>> /* Check arguments */
>> - if (argc != 1) {
>> + if (argc != 2) {
>> ti->error = "Invalid argument count";
>> return -EINVAL;
>> }
>> @@ -774,8 +776,16 @@ static int dmz_ctr(struct dm_target *ti, unsigned int argc, char **argv)
>> }
>> ti->private = dmz;
>>
>> + /* Get the metadata block device */
>> + ret = dm_get_device(ti, argv[0], dm_table_get_mode(ti->table),
>> + &dmz->metadata_dev);
>> + if (ret) {
>> + dmz->metadata_dev = NULL;
>> + goto err;
>> + }
>> +
>> /* Get the target zoned block device */
>> - ret = dmz_get_zoned_device(ti, argv[0]);
>> + ret = dmz_get_zoned_device(ti, argv[1]);
>> if (ret) {
>> dmz->ddev = NULL;
>> goto err;
>> @@ -856,6 +866,7 @@ static int dmz_ctr(struct dm_target *ti, unsigned int argc, char **argv)
>> err_dev:
>> dmz_put_zoned_device(ti);
>> err:
>> + dm_put_device(ti, dmz->metadata_dev);
>> kfree(dmz);
>>
>> return ret;
>> diff --git a/drivers/md/dm-zoned.h b/drivers/md/dm-zoned.h
>> index 5b5e493..e789ff5 100644
>> --- a/drivers/md/dm-zoned.h
>> +++ b/drivers/md/dm-zoned.h
>> @@ -50,6 +50,7 @@
>> */
>> struct dmz_dev {
>> struct block_device *bdev;
>> + struct block_device *meta_bdev;
>>
>> char name[BDEVNAME_SIZE];
>>
>>
--
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