Commit c4a69ecd authored by Mike Snitzer's avatar Mike Snitzer Committed by Alasdair G Kergon
Browse files

dm thin: relax hard limit on the maximum size of a metadata device 



The thin metadata format can only make use of a device that is <=
THIN_METADATA_MAX_SECTORS (currently 15.9375 GB).  Therefore, there is no
practical benefit to using a larger device.

However, it may be that other factors impose a certain granularity for
the space that is allocated to a device (E.g. lvm2 can impose a coarse
granularity through the use of large, >= 1 GB, physical extents).

Rather than reject a larger metadata device, during thin-pool device
construction, switch to allowing it but issue a warning if a device
larger than THIN_METADATA_MAX_SECTORS_WARNING (16 GB) is
provided.  Any space over 15.9375 GB will not be used.

Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
Signed-off-by: default avatarAlasdair G Kergon <agk@redhat.com>
parent 71fd5ae2

Documentation/device-mapper/thin-provisioning.txt

+5 −3
Original line number Diff line number Diff line
@@ -75,10 +75,12 @@ less sharing than average you'll need a larger-than-average metadata device. 


As a guide, we suggest you calculate the number of bytes to use in the

metadata device as 48 * $data_dev_size / $data_block_size but round it up

to 2MB if the answer is smaller.  The largest size supported is 16GB.

to 2MB if the answer is smaller.  If you're creating large numbers of

snapshots which are recording large amounts of change, you may find you

need to increase this.



If you're creating large numbers of snapshots which are recording large

amounts of change, you may need find you need to increase this.

The largest size supported is 16GB: If the device is larger,

a warning will be issued and the excess space will not be used.



Reloading a pool table

----------------------

drivers/md/dm-thin-metadata.c

+3 −0
Original line number Diff line number Diff line
@@ -713,6 +713,9 @@ struct dm_pool_metadata *dm_pool_metadata_open(struct block_device *bdev, 
	if (r)

		goto bad;



	if (bdev_size > THIN_METADATA_MAX_SECTORS)

		bdev_size = THIN_METADATA_MAX_SECTORS;



	disk_super = dm_block_data(sblock);

	disk_super->magic = cpu_to_le64(THIN_SUPERBLOCK_MAGIC);

	disk_super->version = cpu_to_le32(THIN_VERSION);

drivers/md/dm-thin-metadata.h

+13 −0
Original line number Diff line number Diff line
@@ -11,6 +11,19 @@ 


#define THIN_METADATA_BLOCK_SIZE 4096



/*

 * The metadata device is currently limited in size.

 *

 * We have one block of index, which can hold 255 index entries.  Each

 * index entry contains allocation info about 16k metadata blocks.

 */

#define THIN_METADATA_MAX_SECTORS (255 * (1 << 14) * (THIN_METADATA_BLOCK_SIZE / (1 << SECTOR_SHIFT)))



/*

 * A metadata device larger than 16GB triggers a warning.

 */

#define THIN_METADATA_MAX_SECTORS_WARNING (16 * (1024 * 1024 * 1024 >> SECTOR_SHIFT))



/*----------------------------------------------------------------*/



struct dm_pool_metadata;

drivers/md/dm-thin.c

+4 −15
Original line number Diff line number Diff line
@@ -32,16 +32,6 @@ 
#define DATA_DEV_BLOCK_SIZE_MIN_SECTORS (64 * 1024 >> SECTOR_SHIFT)

#define DATA_DEV_BLOCK_SIZE_MAX_SECTORS (1024 * 1024 * 1024 >> SECTOR_SHIFT)



/*

 * The metadata device is currently limited in size.  The limitation is

 * checked lower down in dm-space-map-metadata, but we also check it here

 * so we can fail early.

 *

 * We have one block of index, which can hold 255 index entries.  Each

 * index entry contains allocation info about 16k metadata blocks.

 */

#define METADATA_DEV_MAX_SECTORS (255 * (1 << 14) * (THIN_METADATA_BLOCK_SIZE / (1 << SECTOR_SHIFT)))



/*

 * Device id is restricted to 24 bits.

 */
@@ -1736,6 +1726,7 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv) 
	dm_block_t low_water_blocks;

	struct dm_dev *metadata_dev;

	sector_t metadata_dev_size;

	char b[BDEVNAME_SIZE];



	/*

	 * FIXME Remove validation from scope of lock.
@@ -1757,11 +1748,9 @@ static int pool_ctr(struct dm_target *ti, unsigned argc, char **argv) 
	}



	metadata_dev_size = i_size_read(metadata_dev->bdev->bd_inode) >> SECTOR_SHIFT;

	if (metadata_dev_size > METADATA_DEV_MAX_SECTORS) {

		ti->error = "Metadata device is too large";

		r = -EINVAL;

		goto out_metadata;

	}

	if (metadata_dev_size > THIN_METADATA_MAX_SECTORS_WARNING)

		DMWARN("Metadata device %s is larger than %u sectors: excess space will not be used.",

		       bdevname(metadata_dev->bdev, b), THIN_METADATA_MAX_SECTORS);



	r = dm_get_device(ti, argv[1], FMODE_READ | FMODE_WRITE, &data_dev);

	if (r) {

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