Hi Mikulas and all,
This is *RFC v2* of the *pcache* series, a persistent-memory backed cache.
Compared with *RFC v1*
<https://lore.kernel.org/lkml/20250414014505.20477-1-dongsheng.y...@linux.dev/>
the most important change is that the whole cache has been *ported to
the Device-Mapper framework* and is now exposed as a regular DM target.
Code:
https://github.com/DataTravelGuide/linux/tree/dm-pcache
Full RFC v2 test results:
https://datatravelguide.github.io/dtg-blog/pcache/pcache_rfc_v2_result/results.html
All 962 xfstests cases passed successfully under four different
pcache configurations.
One of the detailed xfstests run:
https://datatravelguide.github.io/dtg-blog/pcache/pcache_rfc_v2_result/test-results/02-._pcache.py_PcacheTest.test_run-crc-enable-gc-gc0-test_script-xfstests-a515/debug.log
Below is a quick tour through the three layers of the implementation,
followed by an example invocation.
----------------------------------------------------------------------
1. pmem access layer
----------------------------------------------------------------------
* All reads use *copy_mc_to_kernel()* so that uncorrectable media
errors are detected and reported.
* All writes go through *memcpy_flushcache()* to guarantee durability
on real persistent memory.
----------------------------------------------------------------------
2. cache-logic layer (segments / keys / workers)
----------------------------------------------------------------------
Main features
- 16 MiB pmem segments, log-structured allocation.
- Multi-subtree RB-tree index for high parallelism.
- Optional per-entry *CRC32* on cached data.
- Background *write-back* worker and watermark-driven *GC*.
- Crash-safe replay: key-sets are scanned from *key_tail* on start-up.
Current limitations
- Only *write-back* mode implemented.
- Only FIFO cache invalidate; other (LRU, ARC...) planned.
----------------------------------------------------------------------
3. dm-pcache target integration
----------------------------------------------------------------------
* Table line
`pcache <pmem_dev> <origin_dev> writeback <true|false>`
* Features advertised to DM:
- `ti->flush_supported = true`, so *PREFLUSH* and *FUA* are honoured
(they force all open key-sets to close and data to be durable).
* Not yet supported:
- Discard / TRIM.
- dynamic `dmsetup reload`.
Runtime controls
- `dmsetup message <dev> 0 gc_percent <0-90>` adjusts the GC trigger.
Status line reports super-block flags, segment counts, GC threshold and
the three tail/head pointers (see the RST document for details).
----------------------------------------------------------------------
Example
----------------------------------------------------------------------
# 1. create a pmem and ssd
pmem=/dev/pmem0
ssd=/dev/sdb
# 2. map a pcache device in front.
dmsetup create pcache_sdb --table \
"0 $(blockdev --getsz $ssd) pcache $pmem $ssd writeback true"
# 3. format and mount
mkfs.ext4 /dev/mapper/pcache_sdb
mount /dev/mapper/pcache_sdb /mnt
# 4. tune GC to 80 %
dmsetup message pcache_sdb 0 gc_percent 80
# 5. monitor
watch -n1 'dmsetup status pcache_sdb'
Testing:
The test suite for pcache is hosted in the dtg-tests project, built
on top of the Avocado Framework. It includes currently:
- Management-related test cases for pcache devices.
- Data verification and validation tests.
- Complete execution of xfstests suite under multiple
configurations.
Thanx
Dongsheng
Dongsheng Yang (11):
dm-pcache: add pcache_internal.h
dm-pcache: add backing device management
dm-pcache: add cache device
dm-pcache: add segment layer
dm-pcache: add cache_segment
dm-pcache: add cache_writeback
dm-pcache: add cache_gc
dm-pcache: add cache_key
dm-pcache: add cache_req
dm-pcache: add cache core
dm-pcache: initial dm-pcache target
.../admin-guide/device-mapper/dm-pcache.rst | 200 ++++
MAINTAINERS | 9 +
drivers/md/Kconfig | 2 +
drivers/md/Makefile | 1 +
drivers/md/dm-pcache/Kconfig | 17 +
drivers/md/dm-pcache/Makefile | 3 +
drivers/md/dm-pcache/backing_dev.c | 305 ++++++
drivers/md/dm-pcache/backing_dev.h | 84 ++
drivers/md/dm-pcache/cache.c | 443 +++++++++
drivers/md/dm-pcache/cache.h | 601 ++++++++++++
drivers/md/dm-pcache/cache_dev.c | 310 ++++++
drivers/md/dm-pcache/cache_dev.h | 70 ++
drivers/md/dm-pcache/cache_gc.c | 170 ++++
drivers/md/dm-pcache/cache_key.c | 907 ++++++++++++++++++
drivers/md/dm-pcache/cache_req.c | 810 ++++++++++++++++
drivers/md/dm-pcache/cache_segment.c | 300 ++++++
drivers/md/dm-pcache/cache_writeback.c | 239 +++++
drivers/md/dm-pcache/dm_pcache.c | 388 ++++++++
drivers/md/dm-pcache/dm_pcache.h | 61 ++
drivers/md/dm-pcache/pcache_internal.h | 116 +++
drivers/md/dm-pcache/segment.c | 63 ++
drivers/md/dm-pcache/segment.h | 74 ++
22 files changed, 5173 insertions(+)
create mode 100644 Documentation/admin-guide/device-mapper/dm-pcache.rst
create mode 100644 drivers/md/dm-pcache/Kconfig
create mode 100644 drivers/md/dm-pcache/Makefile
create mode 100644 drivers/md/dm-pcache/backing_dev.c
create mode 100644 drivers/md/dm-pcache/backing_dev.h
create mode 100644 drivers/md/dm-pcache/cache.c
create mode 100644 drivers/md/dm-pcache/cache.h
create mode 100644 drivers/md/dm-pcache/cache_dev.c
create mode 100644 drivers/md/dm-pcache/cache_dev.h
create mode 100644 drivers/md/dm-pcache/cache_gc.c
create mode 100644 drivers/md/dm-pcache/cache_key.c
create mode 100644 drivers/md/dm-pcache/cache_req.c
create mode 100644 drivers/md/dm-pcache/cache_segment.c
create mode 100644 drivers/md/dm-pcache/cache_writeback.c
create mode 100644 drivers/md/dm-pcache/dm_pcache.c
create mode 100644 drivers/md/dm-pcache/dm_pcache.h
create mode 100644 drivers/md/dm-pcache/pcache_internal.h
create mode 100644 drivers/md/dm-pcache/segment.c
create mode 100644 drivers/md/dm-pcache/segment.h
--
2.34.1
