kernel/Documentation/admin-guide/device-mapper/index.rst, branch linux-rolling-stable

dm-pcache: add persistent cache target in device-mapper

2025-08-25T13:25:29Z

This patch introduces dm-pcache, a new DM target that places a DAX- capable persistent-memory device in front of any slower block device and uses it as a high-throughput, low-latency cache. Design highlights ----------------- - DAX data path – data is copied directly between DRAM and the pmem mapping, bypassing the block layer’s overhead. - Segmented, crash-consistent layout - all layout metadata are dual-replicated CRC-protected. - atomic kset flushes; key replay on mount guarantees cache integrity even after power loss. - Striped multi-tree index - Multi‑tree indexing for high parallelism. - overlap-resolution logic ensures non-intersecting cached extents. - Background services - write-back worker flushes dirty keys in order, preserving backing-device crash consistency. This is important for checkpoint in cloud storage. - garbage collector reclaims clean segments when utilisation exceeds a tunable threshold. - Data integrity – optional CRC32 on cached payload; metadata always protected. Comparison with existing block-level caches --------------------------------------------------------------------------------------------------------------------------------- | Feature | pcache (this patch) | bcache | dm-writecache | |----------------------------------|---------------------------------|------------------------------|---------------------------| | pmem access method | DAX | bio (block I/O) | DAX | | Write latency (4 K rand-write) | ~5 µs | ~20 µs | ~5 µs | | Concurrency | multi subtree index | global index tree | single tree + wc_lock | | IOPS (4K randwrite, 32 numjobs) | 2.1 M | 352 K | 283 K | | Read-cache support | YES | YES | NO | | Deployment | no re-format of backend | backend devices must be | no re-format of backend | | | | reformatted | | | Write-back ordering | log-structured; | no ordering guarantee | no ordering guarantee | | | preserves app-IO-order | | | | Data integrity checks | metadata + data CRC(optional) | metadata CRC only | none | --------------------------------------------------------------------------------------------------------------------------------- Signed-off-by: Dongsheng Yang Signed-off-by: Mikulas Patocka

dm vdo: add vdo documentation to device-mapper index

2024-02-20T18:43:18Z

Signed-off-by: Matthew Sakai Signed-off-by: Mike Snitzer

dm: add documentation for IMA measurement support

2021-08-10T17:34:23Z

To interpret various DM target measurement data in IMA logs, a separate documentation page is needed under Documentation/admin-guide/device-mapper. Add documentation to help system administrators and attestation client/server component owners to interpret the measurement data generated by various DM targets, on various device/table state changes. Signed-off-by: Tushar Sugandhi Signed-off-by: Mike Snitzer

docs: device-mapper: add dm-ebs.rst to an index file

2020-06-19T16:21:56Z

Solves this Sphinx warning: Documentation/admin-guide/device-mapper/dm-ebs.rst: WARNING: document isn't included in any toctree Signed-off-by: Mauro Carvalho Chehab Signed-off-by: Mike Snitzer

Merge tag 'for-5.5/dm-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm

2019-12-13T22:13:15Z

Pull device mapper fixes from Mike Snitzer: - Fix DM multipath by restoring full path selector functionality for bio-based configurations that don't haave a SCSI device handler. - Fix dm-btree removal to ensure non-root btree nodes have at least (max_entries / 3) entries. This resolves userspace thin_check utility's report of "too few entries in btree_node". - Fix both the DM thin-provisioning and dm-clone targets to properly flush the data device prior to metadata commit. This resolves the potential for inconsistency across a power loss event when the data device has a volatile writeback cache. - Small documentation fixes to dm-clone and dm-integrity. * tag 'for-5.5/dm-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm: docs: dm-integrity: remove reference to ARC4 dm thin: Flush data device before committing metadata dm thin metadata: Add support for a pre-commit callback dm clone: Flush destination device before committing metadata dm clone metadata: Use a two phase commit dm clone metadata: Track exact changes per transaction dm btree: increase rebalance threshold in __rebalance2() dm: add dm-clone to the documentation index dm mpath: remove harmful bio-based optimization

dm: add dm-clone to the documentation index

2019-11-26T15:33:50Z

Fixes: 7431b7835f554 ("dm: add clone target") Signed-off-by: Diego Calleja Signed-off-by: Nikos Tsironis Signed-off-by: Mike Snitzer

dm dust: convert documentation to ReST

2019-10-10T17:37:16Z

Convert the dm-dust documentation to ReST formatting, using literal blocks for all of the shell command, shell output, and log output examples. Add dm-dust to index.rst. Additionally, fix an annotation in the "querying for specific bad blocks" section, on the "queryblock ... not found in badblocklist" example, to properly state that the message appears when a given block is not found. Signed-off-by: Bryan Gurney Signed-off-by: Jonathan Corbet

docs: device-mapper: move it to the admin-guide

2019-07-15T14:03:01Z

The DM support describes lots of aspects related to mapped disk partitions from the userspace PoV. Signed-off-by: Mauro Carvalho Chehab