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Subject[PATCH v2 0/3] "Device DAX" for persistent memory
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Date
Changes since v1: [1]

1/ Dropped the lead in cleanup patches from this posting as they appear
on the libnvdimm-for-next branch.

2/ Fixed the needlessly overweight fault locking by replacing it with
rcu_read_lock() and drop taking the i_mmap_lock since it has no effect
or purpose. Unlike block devices the vfs does not arrange for character
device inodes to share the same address_space.

3/ Fixed the device release path since the class release method is not
called when the device is created by device_create_with_groups().

4/ Cleanups resulting from the switch to carry (struct dax_dev *) in
filp->private_date.


---

Device DAX is the device-centric analogue of Filesystem DAX
(CONFIG_FS_DAX). It allows memory ranges to be allocated and mapped
without need of an intervening file system or being bound to block
device semantics.

Why "Device DAX"?

1/ As I mentioned at LSF [2] we are starting to see platforms with
performance and feature differentiated memory ranges. Environments like
high-performance-computing and usages like in-memory databases want
exclusive allocation of a memory range with zero conflicting
kernel/metadata allocations. For dedicated applications of high
bandwidth or low latency memory device-DAX provides a predictable direct
map mechanism.

Note that this is only for the small number of "crazy" applications that
are willing to re-write to get every bit of performance. For everyone
else we, Dave Hansen and I, are looking to add a mechanism to hot-plug
device-DAX ranges into the mm to get general memory management services
(oversubscribe / migration, etc) with the understanding that it may
sacrifice some predictability.

2/ For persistent memory there are similar applications that are willing
to re-write to take full advantage of byte-addressable persistence.
This mechanism satisfies those usages that only need a pre-allocated
file to mmap.

3/ It answers Dave Chinner's call to start thinking about pmem-native
solutions. Device DAX specifically avoids block-device and file system
conflicts.


[1]: https://lists.01.org/pipermail/linux-nvdimm/2016-May/005660.html
[2]: https://lwn.net/Articles/685107/

---

Dan Williams (3):
/dev/dax, pmem: direct access to persistent memory
/dev/dax, core: file operations and dax-mmap
Revert "block: enable dax for raw block devices"


block/ioctl.c | 32 --
drivers/Kconfig | 2
drivers/Makefile | 1
drivers/dax/Kconfig | 26 ++
drivers/dax/Makefile | 4
drivers/dax/dax.c | 568 +++++++++++++++++++++++++++++++++++
drivers/dax/dax.h | 24 +
drivers/dax/pmem.c | 168 ++++++++++
fs/block_dev.c | 96 ++----
include/linux/fs.h | 8
include/uapi/linux/fs.h | 1
mm/huge_memory.c | 1
mm/hugetlb.c | 1
tools/testing/nvdimm/Kbuild | 9 +
tools/testing/nvdimm/config_check.c | 2
15 files changed, 835 insertions(+), 108 deletions(-)
create mode 100644 drivers/dax/Kconfig
create mode 100644 drivers/dax/Makefile
create mode 100644 drivers/dax/dax.c
create mode 100644 drivers/dax/dax.h
create mode 100644 drivers/dax/pmem.c

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