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* dm thin: move bio_prison code to separate moduleMike Snitzer2012-10-121-404/+3
| | | | | | | | | The bio prison code will be useful to other future DM targets so move it to a separate module. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: prepare to separate bio_prison codeMike Snitzer2012-10-121-90/+131
| | | | | | | | | | | The bio prison code will be useful to share with future DM targets. Prepare to move this code into a separate module, adding a dm prefix to structures and functions that will be exported. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: support discard with non power of two block sizeMike Snitzer2012-10-121-10/+13
| | | | | | | | | | | | | | | | | | Support discards when the pool's block size is not a power of 2. The block layer assumes discard_granularity is a power of 2 (in blkdev_issue_discard), so we set this to the largest power of 2 that is a divides into the number of sectors in each block, but never less than DATA_DEV_BLOCK_SIZE_MIN_SECTORS. This patch eliminates the "Discard support must be disabled when the block size is not a power of 2" constraint that was imposed in commit 55f2b8b ("dm thin: support for non power of 2 pool blocksize"). That commit was incomplete: using a block size that is not a power of 2 shouldn't mean disabling discard support on the device completely. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: fix discard support for data devicesMike Snitzer2012-09-261-30/+57
| | | | | | | | | | | | | | | | | | | | | The discard limits that get established for a thin-pool or thin device may be incompatible with the pool's data device. Avoid this by checking the discard limits of the pool's data device. If an incompatibility is found then the pool's 'discard passdown' feature is disabled. Change thin_io_hints to ensure that a thin device always uses the same queue limits as its pool device. Introduce requested_pf to track whether or not the table line originally contained the no_discard_passdown flag and use this directly for table output. We prepare the correct setting for discard_passdown directly in bind_control_target (called from pool_io_hints) and store it in adjusted_pf rather than waiting until we have access to pool->pf in pool_preresume. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: tidy discard supportMike Snitzer2012-09-261-25/+39
| | | | | | | | | | | | | A little thin discard code refactoring to make the next patch (dm thin: fix discard support for data devices) more readable. Pull out a couple of functions (and uses bools instead of unsigned for features). No functional changes. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: do not set discard_zeroes_dataMike Snitzer2012-09-261-1/+1
| | | | | | | | | | | | | | | | | | | The dm thin pool target claims to support the zeroing of discarded data areas. This turns out to be incorrect when processing discards that do not exactly cover a complete number of blocks, so the target must always set discard_zeroes_data_unsupported. The thin pool target will zero blocks when they are allocated if the skip_block_zeroing feature is not specified. The block layer may send a discard that only partly covers a block. If a thin pool block is partially discarded then there is no guarantee that the discarded data will get zeroed before it is accessed again. Due to this, thin devices cannot claim discards will always zero data. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Joe Thornber <ejt@redhat.com> Cc: stable@vger.kernel.org # 3.4+ Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: commit before gathering statusAlasdair G Kergon2012-07-271-2/+7
| | | | | | | | | | | | | | | | Commit outstanding metadata before returning the status for a dm thin pool so that the numbers reported are as up-to-date as possible. The commit is not performed if the device is suspended or if the DM_NOFLUSH_FLAG is supplied by userspace and passed to the target through a new 'status_flags' parameter in the target's dm_status_fn. The userspace dmsetup tool will support the --noflush flag with the 'dmsetup status' and 'dmsetup wait' commands from version 1.02.76 onwards. Tested-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: add read only and fail io modesJoe Thornber2012-07-271-95/+321
| | | | | | | | | | | | | | | Add read-only and fail-io modes to thin provisioning. If a transaction commit fails the pool's metadata device will transition to "read-only" mode. If a commit fails once already in read-only mode the transition to "fail-io" mode occurs. Once in fail-io mode the pool and all associated thin devices will report a status of "Fail". Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: reduce number of metadata commitsJoe Thornber2012-07-271-1/+7
| | | | | | | | | | Reduce the number of metadata commits by using dm_thin_changed_this_transaction to check if metadata was changed on a per thin device granularity. Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin metadata: add format option to dm_pool_metadata_openJoe Thornber2012-07-271-1/+1
| | | | | | | | | Add a parameter to dm_pool_metadata_open to indicate whether or not an unformatted metadata area should be formatted. Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm: use bool bitfields in struct dm_targetAlasdair G Kergon2012-07-271-4/+4
| | | | | | Use boolean bit fields for flags in struct dm_target. Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: set flush_supportedJoe Thornber2012-07-271-0/+1
| | | | | | | | | | The thin provisioning target commits internal metadata on flush. So it should receive flushes regardless of whether the underlying devices support them. Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: avoid unnecessarily breaking sharing for flushesJoe Thornber2012-07-271-1/+1
| | | | | | | | | There's no need to break sharing, triggering a copy, for a write that has no data (i.e. a flush). Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: fix memory leak in process_prepared_mapping error pathsJoe Thornber2012-07-271-2/+3
| | | | | | | | | | | Fix memory leak in process_prepared_mapping by always freeing the dm_thin_new_mapping structs from the mapping_pool mempool on the error paths. Signed-off-by: Joe Thornber <ejt@redhat.com> Cc: stable@vger.kernel.org Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: optimize power of two block sizeMikulas Patocka2012-07-271-7/+16
| | | | | | | | | | | | | | | | dm-thin will be most likely used with a block size that is a power of two. So it should be optimized for this case. This patch changes division and modulo operations to shifts and bit masks if block size is a power of two. A test that bi_sector is divisible by a block size is removed from io_overlaps_block. Device mapper never sends bios that span a block boundary. Consequently, if we tested that bi_size is equivalent to block size, bi_sector must already be on a block boundary. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: split discards on block boundaryMikulas Patocka2012-07-271-9/+7
| | | | | | | | | | | | | | This patch sets the variable "ti->split_discard_requests" for the dm thin target so that device mapper core splits discard requests on a block boundary. Consequently, a discard request that spans multiple blocks is never sent to dm-thin. The patch also removes some code in process_discard that deals with discards that span multiple blocks. Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: support for non power of 2 pool blocksizeMike Snitzer2012-07-271-22/+37
| | | | | | | | | | | | | | | | | | | | Non power of 2 blocksize support is needed to properly align thinp IO on storage that has non power of 2 optimal IO sizes (e.g. RAID6 10+2). Use sector_div to support non power of 2 blocksize for the pool's data device. This provides comparable performance to the power of 2 math that was performed until now (as tested on modern x86_64 hardware). The kernel currently assumes that limits->discard_granularity is a power of two so the thin target only enables discard support if the block size is a power of two. Eliminate pool structure's 'block_shift', 'offset_mask' and remaining 4 byte holes. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm: support non power of two target max_io_lenMike Snitzer2012-07-271-1/+4
| | | | | | | | | | | | | Remove the restriction that limits a target's specified maximum incoming I/O size to be a power of 2. Rename this setting from 'split_io' to the less-ambiguous 'max_io_len'. Change it from sector_t to uint32_t, which is plenty big enough, and introduce a wrapper function dm_set_target_max_io_len() to set it. Use sector_div() to process it now that it is not necessarily a power of 2. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: provide specific errors for two table load failure casesMike Snitzer2012-07-271-2/+6
| | | | | | | | | | | Provide specific error message strings for two pool_ctr() failure cases that currently give just "Unknown error". Reference: test_two_pools_pointing_to_the_same_metadata_fails and test_different_pool_cant_replace_pool in thinp-test-suite. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: clean up compiler warningMike Snitzer2012-07-271-1/+1
| | | | | | | | | Clean up "warning: dubious: !x & y". Also make it clear that __snapshotted_since() returns a bool and that dm_thin_lookup_result's 'shared' member is a flag. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: reduce endio_hook pool sizeAlasdair G Kergon2012-07-271-1/+1
| | | | | | | | | | | | | Reduce the slab size used for the dm_thin_endio_hook mempool. Allocation has been seen to fail on machines with smaller amounts of memory due to fragmentation. lvm: page allocation failure. order:5, mode:0xd0 device-mapper: table: 253:38: thin-pool: Error creating pool's endio_hook mempool Cc: stable@vger.kernel.org Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: do not send discards to shared blocksMikulas Patocka2012-07-201-1/+5
| | | | | | | | | | | | | | | | | | | | | | When process_discard receives a partial discard that doesn't cover a full block, it sends this discard down to that block. Unfortunately, the block can be shared and the discard would corrupt the other snapshots sharing this block. This patch detects block sharing and ends the discard with success when sending it to the shared block. The above change means that if the device supports discard it can't be guaranteed that a discard request zeroes data. Therefore, we set ti->discard_zeroes_data_unsupported. Thin target discard support with this bug arrived in commit 104655fd4dcebd50068ef30253a001da72e3a081 (dm thin: support discards). Signed-off-by: Mikulas Patocka <mpatocka@redhat.com> Cc: stable@kernel.org Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: commit metadata before creating metadata snapshotJoe Thornber2012-07-031-0/+7
| | | | | | | | | | | | | | | | | | | | | Userland sometimes sees a corrupt metadata block if metadata is changing rapidly when a metadata snapshot is reserved for userland, To make the problem go away, commit before we take the metadata snapshot (which is a sensible thing to do anyway). The checksums mean userland spots this corruption immediately so there's no risk of acting on incorrect data. No corruption exists from the kernel's point of view, and thin_check passes after pool shutdown. I believe this is to do with shared blocks at the first level of the {device, mapping} btree. Prior to the metadata-snap support no sharing at this level was possible, so this patch is only required after commit cc8394d86f045b86ff303d3c9e4ce47d97148951 ("dm thin: provide userspace access to pool metadata"). Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: provide userspace access to pool metadataJoe Thornber2012-06-031-2/+40
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This patch implements two new messages that can be sent to the thin pool target allowing it to take a snapshot of the _metadata_. This, read-only snapshot can be accessed by userland, concurrently with the live target. Only one metadata snapshot can be held at a time. The pool's status line will give the block location for the current msnap. Since version 0.1.5 of the userland thin provisioning tools, the thin_dump program displays the msnap as follows: thin_dump -m <msnap root> <metadata dev> Available here: https://github.com/jthornber/thin-provisioning-tools Now that userland can access the metadata we can do various things that have traditionally been kernel side tasks: i) Incremental backups. By using metadata snapshots we can work out what blocks have changed over time. Combined with data snapshots we can ensure the data doesn't change while we back it up. A short proof of concept script can be found here: https://github.com/jthornber/thinp-test-suite/blob/master/incremental_backup_example.rb ii) Migration of thin devices from one pool to another. iii) Merging snapshots back into an external origin. iv) Asyncronous replication. Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: use slab mempoolsMike Snitzer2012-06-031-62/+99
| | | | | | | | | Use dedicated caches prefixed with a "dm_" name rather than relying on kmalloc mempools backed by generic slab caches so the memory usage of thin provisioning (and any leaks) can be accounted for independently. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: fix table output when pool target disables discard passdown internallyMike Snitzer2012-05-191-15/+17
| | | | | | | | | | | | | | | | | | | | | | When the thin pool target clears the discard_passdown parameter internally, it incorrectly changes the table line reported to userspace. This breaks dumb string comparisons on these table lines in generic userspace device-mapper library code and leads to tables being reloaded repeatedly when nothing is actually meant to be changing. This patch corrects this by no longer changing the table line when discard passdown was disabled. We can still tell when discard passdown is overridden by looking for the message "Discard unsupported by data device (sdX): Disabling discard passdown." This automatic detection is also moved from the 'load' to the 'resume' so that it is re-evaluated should the properties of underlying devices change. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Acked-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: correct module descriptionAlasdair G Kergon2012-05-121-1/+1
| | | | | | | Remove duplicate copy of string "device-mapper" (DM_NAME) from MODULE_DESCRIPTION. Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: fix unprotected use of prepared_discards listMike Snitzer2012-05-121-0/+5
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Fix two places in commit 104655fd4dce ("dm thin: support discards") that didn't use pool->lock to protect against concurrent changes to the prepared_discards list. Without this fix, thin_endio() can race with process_discard(), leading to concurrent list_add()s that result in the processes locking up with an error like the following: WARNING: at lib/list_debug.c:32 __list_add+0x8f/0xa0() ... list_add corruption. next->prev should be prev (ffff880323b96140), but was ffff8801d2c48440. (next=ffff8801d2c485c0). ... Pid: 17205, comm: kworker/u:1 Tainted: G W O 3.4.0-rc3.snitm+ #1 Call Trace: [<ffffffff8103ca1f>] warn_slowpath_common+0x7f/0xc0 [<ffffffff8103cb16>] warn_slowpath_fmt+0x46/0x50 [<ffffffffa04f6ce6>] ? bio_detain+0xc6/0x210 [dm_thin_pool] [<ffffffff8124ff3f>] __list_add+0x8f/0xa0 [<ffffffffa04f70d2>] process_discard+0x2a2/0x2d0 [dm_thin_pool] [<ffffffffa04f6a78>] ? remap_and_issue+0x38/0x50 [dm_thin_pool] [<ffffffffa04f7c3b>] process_deferred_bios+0x7b/0x230 [dm_thin_pool] [<ffffffffa04f7df0>] ? process_deferred_bios+0x230/0x230 [dm_thin_pool] [<ffffffffa04f7e42>] do_worker+0x52/0x60 [dm_thin_pool] [<ffffffff81056fa9>] process_one_work+0x129/0x450 [<ffffffff81059b9c>] worker_thread+0x17c/0x3c0 [<ffffffff81059a20>] ? manage_workers+0x120/0x120 [<ffffffff8105eabe>] kthread+0x9e/0xb0 [<ffffffff814ceda4>] kernel_thread_helper+0x4/0x10 [<ffffffff8105ea20>] ? kthread_freezable_should_stop+0x70/0x70 [<ffffffff814ceda0>] ? gs_change+0x13/0x13 ---[ end trace 7e0a523bc5e52692 ]--- Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: reinstate missing mempool_free in cell_release_singletonMike Snitzer2012-05-121-3/+6
| | | | | | | | | | | | | Fix a significant memory leak inadvertently introduced during simplification of cell_release_singleton() in commit 6f94a4c45a6f744383f9f695dde019998db3df55 ("dm thin: fix stacked bi_next usage"). A cell's hlist_del() must be accompanied by a mempool_free(). Use __cell_release() to do this, like before. Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: add pool target flags to control discardJoe Thornber2012-03-281-27/+108
| | | | | | | | | | | | | Add dm thin target arguments to control discard support. ignore_discard: Disables discard support no_discard_passdown: Don't pass discards down to the underlying data device, but just remove the mapping within the thin provisioning target. Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: support discardsJoe Thornber2012-03-281-14/+158
| | | | | | | | | | | | | | | | | | | | | | Support discards in the thin target. On discard the corresponding mapping(s) are removed from the thin device. If the associated block(s) are no longer shared the discard is passed to the underlying device. All bios other than discards now have an associated deferred_entry that is saved to the 'all_io_entry' in endio_hook. When non-discard IO completes and associated mappings are quiesced any discards that were deferred, via ds_add_work() in process_discard(), will be queued for processing by the worker thread. Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com> drivers/md/dm-thin.c | 173 ++++++++++++++++++++++++++++++++++++++++++++++---- drivers/md/dm-thin.c | 172 ++++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 158 insertions(+), 14 deletions(-)
* dm thin: prepare to support discardJoe Thornber2012-03-281-53/+72
| | | | | | | | | | | | | | | | This patch contains the ground work needed for dm-thin to support discard. - Adds endio function that replaces shared_read_endio. - Introduce an explicit 'quiesced' flag into the new_mapping structure. Before, this was implicitly indicated by m->list being empty. - The map_info->ptr remains constant for the duration of a bio's trip through the thin target. Make it easier to reason about it. Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: use dm_target_offsetAlasdair G Kergon2012-03-281-1/+1
| | | | | | | Use dm_target_offset wrapper instead of referencing the awkward ti->begin explicitly. Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: support read only external snapshot originsJoe Thornber2012-03-281-14/+71
| | | | | | | | | | | | | | | | | Support the use of an external _read only_ device as an origin for a thin device. Any read to an unprovisioned area of the thin device will be passed through to the origin. Writes trigger allocation of new blocks as usual. One possible use case for this would be VM hosts that want to run guests on thinly-provisioned volumes but have the base image on another device (possibly shared between many VMs). Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: relax hard limit on the maximum size of a metadata deviceMike Snitzer2012-03-281-15/+4
| | | | | | | | | | | | | | | | | | 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: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: commit outstanding data every secondJoe Thornber2012-03-281-2/+26
| | | | | | | | | | | | | | | | | Commit unwritten data every second to prevent too much building up. Released blocks don't become available until after the next commit (for crash resilience). Prior to this patch commits were only triggered by a message to the target or a REQ_{FLUSH,FUA} bio. This allowed far too big a position to build up. The interval is hard-coded to 1 second. This is a sensible setting. I'm not making this user configurable, since there isn't much to be gained by tweaking this - and a lot lost by setting it far too high. Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: correct commentsJoe Thornber2012-03-281-1/+1
| | | | | | | | | | | Remove documentation for unimplemented 'trim' message. I'd planned a 'trim' target message for shrinking thin devices, but this is better handled via the discard ioctl. Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm thin: fix stacked bi_next usageJoe Thornber2012-03-281-51/+73
| | | | | | | | | | | | | | | | | | | Avoid using the bi_next field for the holder of a cell when deferring bios because a stacked device below might change it. Store the holder in a new field in struct cell instead. When a cell is created, the bio that triggered creation (the holder) was added to the same bio list as subsequent bios. In some cases we pass this holder bio directly to devices underneath. If those devices use the bi_next field there will be trouble... This also simplifies some code that had to work out which bio was the holder. Signed-off-by: Joe Thornber <ejt@redhat.com> Cc: stable@kernel.org Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
* dm: add thin provisioning targetJoe Thornber2011-10-311-0/+2428
Initial EXPERIMENTAL implementation of device-mapper thin provisioning with snapshot support. The 'thin' target is used to create instances of the virtual devices that are hosted in the 'thin-pool' target. The thin-pool target provides data sharing among devices. This sharing is made possible using the persistent-data library in the previous patch. The main highlight of this implementation, compared to the previous implementation of snapshots, is that it allows many virtual devices to be stored on the same data volume, simplifying administration and allowing sharing of data between volumes (thus reducing disk usage). Another big feature is support for arbitrary depth of recursive snapshots (snapshots of snapshots of snapshots ...). The previous implementation of snapshots did this by chaining together lookup tables, and so performance was O(depth). This new implementation uses a single data structure so we don't get this degradation with depth. For further information and examples of how to use this, please read Documentation/device-mapper/thin-provisioning.txt Signed-off-by: Joe Thornber <thornber@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
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