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Subject[PATCH 00/22] add Object Storage Media Pool (mpool)
From: Nabeel M Mohamed <>

This patch series introduces the mpool object storage media pool driver.
Mpool implements a simple transactional object store on top of block
storage devices.

Mpool was developed for the Heterogeneous-Memory Storage Engine (HSE)
project, which is a high-performance key-value storage engine designed
for SSDs. HSE stores its data exclusively in mpool.

Mpool is readily applicable to other storage systems built on immutable
objects. For example, the many databases that store records in
immutable SSTables organized as an LSM-tree or similar data structure.

We developed mpool for HSE storage, versus using a file system or raw
block device, for several reasons.

A primary motivator was the need for a storage model that maps naturally
to conventional block storage devices, as well as to emerging device
interfaces we plan to support in the future, such as
* NVMe Zoned Namespaces (ZNS)
* NVMe Streams
* Persistent memory accessed via CXL or similar technologies

Another motivator was the need for a storage model that readily supports
multiple classes of storage devices or media in a single storage pool,
such as
* QLC SSDs for storing the bulk of objects, and
* 3DXP SSDs or persistent memory for storing objects requiring
low-latency access

The mpool object storage model meets these needs. It also provides
other features that benefit storage systems built on immutable objects,
* Facilities to memory-map a specified collection of objects into a
linear address space
* Concurrent access to object data directly and memory-mapped to greatly
reduce page cache pollution from background operations such as
LSM-tree compaction
* Proactive eviction of object data from the page cache, based on
object-level metrics, to avoid excessive memory pressure and its
associated performance impacts
* High concurrency and short code paths for efficient access to
low-latency storage devices

HSE takes advantage of all these mpool features to achieve high
throughput with low tail-latencies.

Mpool is implemented as a character device driver where
* /dev/mpoolctl is the control file (minor number 0) supporting mpool
management ioctls
* /dev/mpool/<mpool-name> are mpool files (minor numbers >0), one per
mpool, supporting object management ioctls

CLI/UAPI access to /dev/mpoolctl and /dev/mpool/<mpool-name> are
controlled by their UID, GID, and mode bits. To provide a familiar look
and feel, the mpool management model and CLI are intentionally aligned
to those of LVM to the degree practical.

An mpool is created with a block storage device specified for its
required capacity media class, and optionally a second block storage
device specified for its staging media class. We recommend virtual
block devices (such as LVM logical volumes) to aggregate the performance
and capacity of multiple physical block devices, to enable sharing of
physical block devices between mpools (or for other uses), and to
support extending the size of a block device used for an mpool media
class. The libblkid library recognizes mpool formatted block devices as
of util-linux v2.32.

Mpool implements a transactional object store with two simple object
abstractions: mblocks and mlogs.

Mblock objects are containers comprising a linear sequence of bytes that
can be written exactly once, are immutable after writing, and can be
read in whole or in part as needed until deleted. Mblocks in a media
class are currently fixed size, which is configured when an mpool is
created, though the amount of data written to mblocks will differ.

Mlog objects are containers for record logging. Records of arbitrary
size can be appended to an mlog until it is full. Once full, an mlog
must be erased before additional records can be appended. Mlog records
can be read sequentially from the beginning at any time. Mlogs in a
media class are always a multiple of the mblock size for that media

Mblock and mlog writes avoid the page cache. Mblocks are written,
committed, and made immutable before they can be read either directly
(avoiding the page cache) or mmaped. Mlogs are always read and updated
directly (avoiding the page cache) and cannot be mmaped.

Mpool also provides the metadata container (MDC) APIs that clients can
use to simplify storing and maintaining metadata. These MDC APIs are
helper functions built on a pair of mlogs per MDC.

The mpool Wiki contains full details on the
* Management model in the "Configure mpools" section
* Object model in the "Develop mpool Applications" section
* Kernel module architecture in the "Explore mpool Internals" section,
which provides context for reviewing this patch series


The mpool UAPI and kernel module (not the patchset) are available on
GitHub at:

The HSE key-value storage engine is available on GitHub at:

Nabeel M Mohamed (22):
mpool: add utility routines and ioctl definitions
mpool: add in-memory struct definitions
mpool: add on-media struct definitions
mpool: add pool drive component which handles mpool IO using the block
layer API
mpool: add space map component which manages free space on mpool
mpool: add on-media pack, unpack and upgrade routines
mpool: add superblock management routines
mpool: add pool metadata routines to manage object lifecycle and IO
mpool: add mblock lifecycle management and IO routines
mpool: add mlog IO utility routines
mpool: add mlog lifecycle management and IO routines
mpool: add metadata container or mlog-pair framework
mpool: add utility routines for mpool lifecycle management
mpool: add pool metadata routines to create persistent mpools
mpool: add mpool lifecycle management routines
mpool: add mpool control plane utility routines
mpool: add mpool lifecycle management ioctls
mpool: add object lifecycle management ioctls
mpool: add support to mmap arbitrary collection of mblocks
mpool: add support to proactively evict cached mblock data from the
mpool: add documentation
mpool: add Kconfig and Makefile

drivers/Kconfig | 2 +
drivers/Makefile | 1 +
drivers/mpool/Kconfig | 28 +
drivers/mpool/Makefile | 11 +
drivers/mpool/assert.h | 25 +
drivers/mpool/init.c | 126 ++
drivers/mpool/init.h | 17 +
drivers/mpool/mblock.c | 432 +++++
drivers/mpool/mblock.h | 161 ++
drivers/mpool/mcache.c | 1036 ++++++++++++
drivers/mpool/mcache.h | 102 ++
drivers/mpool/mclass.c | 103 ++
drivers/mpool/mclass.h | 137 ++
drivers/mpool/mdc.c | 486 ++++++
drivers/mpool/mdc.h | 106 ++
drivers/mpool/mlog.c | 1667 ++++++++++++++++++
drivers/mpool/mlog.h | 212 +++
drivers/mpool/mlog_utils.c | 1352 +++++++++++++++
drivers/mpool/mlog_utils.h | 63 +
drivers/mpool/mp.c | 1086 ++++++++++++
drivers/mpool/mp.h | 231 +++
drivers/mpool/mpcore.c | 987 +++++++++++
drivers/mpool/mpcore.h | 354 ++++
drivers/mpool/mpctl.c | 2801 +++++++++++++++++++++++++++++++
drivers/mpool/mpctl.h | 59 +
drivers/mpool/mpool-locking.rst | 90 +
drivers/mpool/mpool_ioctl.h | 636 +++++++
drivers/mpool/mpool_printk.h | 44 +
drivers/mpool/omf.c | 1320 +++++++++++++++
drivers/mpool/omf.h | 593 +++++++
drivers/mpool/omf_if.h | 381 +++++
drivers/mpool/params.h | 116 ++
drivers/mpool/pd.c | 426 +++++
drivers/mpool/pd.h | 202 +++
drivers/mpool/pmd.c | 2046 ++++++++++++++++++++++
drivers/mpool/pmd.h | 379 +++++
drivers/mpool/pmd_obj.c | 1569 +++++++++++++++++
drivers/mpool/pmd_obj.h | 499 ++++++
drivers/mpool/reaper.c | 692 ++++++++
drivers/mpool/reaper.h | 71 +
drivers/mpool/sb.c | 625 +++++++
drivers/mpool/sb.h | 162 ++
drivers/mpool/smap.c | 1031 ++++++++++++
drivers/mpool/smap.h | 334 ++++
drivers/mpool/sysfs.c | 48 +
drivers/mpool/sysfs.h | 48 +
drivers/mpool/upgrade.c | 138 ++
drivers/mpool/upgrade.h | 128 ++
drivers/mpool/uuid.h | 59 +
49 files changed, 23222 insertions(+)
create mode 100644 drivers/mpool/Kconfig
create mode 100644 drivers/mpool/Makefile
create mode 100644 drivers/mpool/assert.h
create mode 100644 drivers/mpool/init.c
create mode 100644 drivers/mpool/init.h
create mode 100644 drivers/mpool/mblock.c
create mode 100644 drivers/mpool/mblock.h
create mode 100644 drivers/mpool/mcache.c
create mode 100644 drivers/mpool/mcache.h
create mode 100644 drivers/mpool/mclass.c
create mode 100644 drivers/mpool/mclass.h
create mode 100644 drivers/mpool/mdc.c
create mode 100644 drivers/mpool/mdc.h
create mode 100644 drivers/mpool/mlog.c
create mode 100644 drivers/mpool/mlog.h
create mode 100644 drivers/mpool/mlog_utils.c
create mode 100644 drivers/mpool/mlog_utils.h
create mode 100644 drivers/mpool/mp.c
create mode 100644 drivers/mpool/mp.h
create mode 100644 drivers/mpool/mpcore.c
create mode 100644 drivers/mpool/mpcore.h
create mode 100644 drivers/mpool/mpctl.c
create mode 100644 drivers/mpool/mpctl.h
create mode 100644 drivers/mpool/mpool-locking.rst
create mode 100644 drivers/mpool/mpool_ioctl.h
create mode 100644 drivers/mpool/mpool_printk.h
create mode 100644 drivers/mpool/omf.c
create mode 100644 drivers/mpool/omf.h
create mode 100644 drivers/mpool/omf_if.h
create mode 100644 drivers/mpool/params.h
create mode 100644 drivers/mpool/pd.c
create mode 100644 drivers/mpool/pd.h
create mode 100644 drivers/mpool/pmd.c
create mode 100644 drivers/mpool/pmd.h
create mode 100644 drivers/mpool/pmd_obj.c
create mode 100644 drivers/mpool/pmd_obj.h
create mode 100644 drivers/mpool/reaper.c
create mode 100644 drivers/mpool/reaper.h
create mode 100644 drivers/mpool/sb.c
create mode 100644 drivers/mpool/sb.h
create mode 100644 drivers/mpool/smap.c
create mode 100644 drivers/mpool/smap.h
create mode 100644 drivers/mpool/sysfs.c
create mode 100644 drivers/mpool/sysfs.h
create mode 100644 drivers/mpool/upgrade.c
create mode 100644 drivers/mpool/upgrade.h
create mode 100644 drivers/mpool/uuid.h


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