Re: [resend PATCH v2 00/33] dax: introduce dax_operations

[Dan Williams]

[ adding akpm, sfr, and jens ]

I applied this series and pushed it out for the nvdimm.git branch that
gets auto pulled into -next. The set is still awaiting acks from
device-mapper, ext4, xfs, and vfs (for the copy_from_iter_ops, patch
29/33). If those come next week perhaps this can be merged for 4.12,
but if not this will need to wait until 4.13.

There are some minor collisions with Al's copy_from_user rework, the
new dax tracepoints, and the removal of discard support from the brd
driver. A sample merge is available here:

https://git.kernel.org/pub/scm/linux/kernel/git/nvdimm/nvdimm.git/log/?h=libnvdimm-for-4.12-merge

If it causes any other problems just drop and I'll retry for 4.13.

On Mon, Apr 17, 2017 at 12:08 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> [ resend to add dm-devel, linux-block, and fs-devel, apologies for the
> duplicates ]
>
> Changes since v1 [1] and the dax-fs RFC [2]:
> * rename struct dax_inode to struct dax_device (Christoph)
> * rewrite arch_memcpy_to_pmem() in C with inline asm
> * use QUEUE_FLAG_WC to gate dax cache management (Jeff)
> * add device-mapper plumbing for the ->copy_from_iter() and ->flush()
>   dax_operations
> * kill struct blk_dax_ctl and bdev_direct_access (Christoph)
> * cleanup the ->direct_access() calling convention to be page based
>   (Christoph)
> * introduce dax_get_by_host() and don't pollute struct super_block with
>   dax_device details (Christoph)
>
> [1]: https://lists.01.org/pipermail/linux-nvdimm/2017-January/008586.html
> [2]: https://lwn.net/Articles/713064/
>
> ---
> A few months back, in the course of reviewing the memcpy_nocache()
> proposal from Brian, Linus proposed that the pmem specific
> memcpy_to_pmem() routine be moved to be implemented at the driver level
> [3]:
>
>    "Quite frankly, the whole 'memcpy_nocache()' idea or (ab-)using
>     copy_user_nocache() just needs to die. It's idiotic.
>
>     As you point out, it's also fundamentally buggy crap.
>
>     Throw it away. There is no possible way this is ever valid or
>     portable. We're not going to lie and claim that it is.
>
>     If some driver ends up using 'movnt' by hand, that is up to that
>     *driver*. But no way in hell should we care about this one whit in
>     the sense of <linux/uaccess.h>."
>
> This feedback also dovetails with another fs/dax.c design wart of being
> hard coded to assume the backing device is pmem. We call the pmem
> specific copy, clear, and flush routines even if the backing device
> driver is one of the other 3 dax drivers (axonram, dccssblk, or brd).
> There is no reason to spend cpu cycles flushing the cache after writing
> to brd, for example, since it is using volatile memory for storage.
>
> Moreover, the pmem driver might be fronting a volatile memory range
> published by the ACPI NFIT, or the platform might have arranged to flush
> cpu caches on power fail. This latter capability is a feature that has
> appeared in embedded storage appliances (pre-ACPI-NFIT nvdimm
> platforms).
>
> So, this series:
>
> 1/ moves what was previously named "the pmem api" out of the global
>    namespace and into drivers that need to be concerned with
>    architecture specific persistent memory considerations.
>
> 2/ arranges for dax to stop abusing __copy_user_nocache() and implements
>    a libnvdimm-local memcpy that uses 'movnt' on x86_64. This might be
>    expanded in the future to use 'movntdqa' if the copy size is above
>    some threshold, or expanded with support for other architectures [4].
>
> 3/ makes cache maintenance optional by arranging for dax to call driver
>    specific copy and flush operations only if the driver publishes them.
>
> 4/ allows filesytem-dax cache management to be controlled by the block
>    device write-cache queue flag. The pmem driver is updated to clear
>    that flag by default when pmem is driving volatile memory.
>
> [3]: https://lists.01.org/pipermail/linux-nvdimm/2017-January/008364.html
> [4]: https://lists.01.org/pipermail/linux-nvdimm/2017-April/009478.html
>
> These patches have been through a round of build regression fixes
> notified by the 0day robot. All review welcome, but the patches that
> need extra attention are the device-mapper and uio changes
> (copy_from_iter_ops).
>
> This series is based on a merge of char-misc-next (for cdev api reworks)
> and libnvdimm-fixes (dax locking and __copy_user_nocache fixes).
>
> ---
>
> Dan Williams (33):
>       device-dax: rename 'dax_dev' to 'dev_dax'
>       dax: refactor dax-fs into a generic provider of 'struct dax_device' instances
>       dax: add a facility to lookup a dax device by 'host' device name
>       dax: introduce dax_operations
>       pmem: add dax_operations support
>       axon_ram: add dax_operations support
>       brd: add dax_operations support
>       dcssblk: add dax_operations support
>       block: kill bdev_dax_capable()
>       dax: introduce dax_direct_access()
>       dm: add dax_device and dax_operations support
>       dm: teach dm-targets to use a dax_device + dax_operations
>       ext2, ext4, xfs: retrieve dax_device for iomap operations
>       Revert "block: use DAX for partition table reads"
>       filesystem-dax: convert to dax_direct_access()
>       block, dax: convert bdev_dax_supported() to dax_direct_access()
>       block: remove block_device_operations ->direct_access()
>       x86, dax, pmem: remove indirection around memcpy_from_pmem()
>       dax, pmem: introduce 'copy_from_iter' dax operation
>       dm: add ->copy_from_iter() dax operation support
>       filesystem-dax: convert to dax_copy_from_iter()
>       dax, pmem: introduce an optional 'flush' dax_operation
>       dm: add ->flush() dax operation support
>       filesystem-dax: convert to dax_flush()
>       x86, dax: replace clear_pmem() with open coded memset + dax_ops->flush
>       x86, dax, libnvdimm: move wb_cache_pmem() to libnvdimm
>       x86, libnvdimm, pmem: move arch_invalidate_pmem() to libnvdimm
>       x86, libnvdimm, dax: stop abusing __copy_user_nocache
>       uio, libnvdimm, pmem: implement cache bypass for all copy_from_iter() operations
>       libnvdimm, pmem: fix persistence warning
>       libnvdimm, nfit: enable support for volatile ranges
>       filesystem-dax: gate calls to dax_flush() on QUEUE_FLAG_WC
>       libnvdimm, pmem: disable dax flushing when pmem is fronting a volatile region
>
>
>  MAINTAINERS                      |    2
>  arch/powerpc/platforms/Kconfig   |    1
>  arch/powerpc/sysdev/axonram.c    |   45 +++-
>  arch/x86/Kconfig                 |    1
>  arch/x86/include/asm/pmem.h      |  141 ------------
>  arch/x86/include/asm/string_64.h |    1
>  block/Kconfig                    |    1
>  block/partition-generic.c        |   17 -
>  drivers/Makefile                 |    2
>  drivers/acpi/nfit/core.c         |   15 +
>  drivers/block/Kconfig            |    1
>  drivers/block/brd.c              |   52 +++-
>  drivers/dax/Kconfig              |   10 +
>  drivers/dax/Makefile             |    5
>  drivers/dax/dax.h                |   15 -
>  drivers/dax/device-dax.h         |   25 ++
>  drivers/dax/device.c             |  415 +++++++++++------------------------
>  drivers/dax/pmem.c               |   10 -
>  drivers/dax/super.c              |  445 ++++++++++++++++++++++++++++++++++++++
>  drivers/md/Kconfig               |    1
>  drivers/md/dm-core.h             |    1
>  drivers/md/dm-linear.c           |   53 ++++-
>  drivers/md/dm-snap.c             |    6 -
>  drivers/md/dm-stripe.c           |   65 ++++--
>  drivers/md/dm-target.c           |    6 -
>  drivers/md/dm.c                  |  112 ++++++++--
>  drivers/nvdimm/Kconfig           |    6 +
>  drivers/nvdimm/Makefile          |    1
>  drivers/nvdimm/bus.c             |   10 -
>  drivers/nvdimm/claim.c           |    9 -
>  drivers/nvdimm/core.c            |    2
>  drivers/nvdimm/dax_devs.c        |    2
>  drivers/nvdimm/dimm_devs.c       |    2
>  drivers/nvdimm/namespace_devs.c  |    9 -
>  drivers/nvdimm/nd-core.h         |    9 +
>  drivers/nvdimm/pfn_devs.c        |    4
>  drivers/nvdimm/pmem.c            |   82 +++++--
>  drivers/nvdimm/pmem.h            |   26 ++
>  drivers/nvdimm/region_devs.c     |   39 ++-
>  drivers/nvdimm/x86.c             |  155 +++++++++++++
>  drivers/s390/block/Kconfig       |    1
>  drivers/s390/block/dcssblk.c     |   44 +++-
>  fs/block_dev.c                   |  117 +++-------
>  fs/dax.c                         |  302 ++++++++++++++------------
>  fs/ext2/inode.c                  |    9 +
>  fs/ext4/inode.c                  |    9 +
>  fs/iomap.c                       |    3
>  fs/xfs/xfs_iomap.c               |   10 +
>  include/linux/blkdev.h           |   19 --
>  include/linux/dax.h              |   43 +++-
>  include/linux/device-mapper.h    |   14 +
>  include/linux/iomap.h            |    1
>  include/linux/libnvdimm.h        |   10 +
>  include/linux/pmem.h             |  165 --------------
>  include/linux/string.h           |    8 +
>  include/linux/uio.h              |    4
>  lib/Kconfig                      |    6 -
>  lib/iov_iter.c                   |   25 ++
>  tools/testing/nvdimm/Kbuild      |   11 +
>  tools/testing/nvdimm/pmem-dax.c  |   21 +-
>  60 files changed, 1584 insertions(+), 1042 deletions(-)
>  delete mode 100644 arch/x86/include/asm/pmem.h
>  create mode 100644 drivers/dax/device-dax.h
>  rename drivers/dax/{dax.c => device.c} (60%)
>  create mode 100644 drivers/dax/super.c
>  create mode 100644 drivers/nvdimm/x86.c
>  delete mode 100644 include/linux/pmem.h