Changes since v8 [1]: * Move MAP_SHARED_VALIDATE definition next to MAP_SHARED in all arch headers (Jan) * Include xfs_layout.h directly in all the files that call xfs_break_layouts() (Dave) * Clarify / add more comments to the MAP_DIRECT checks at fault time (Dave) * Rename iomap_can_allocate() to break_layouts_nowait() to make it plain the reason we are bailing out of iomap_begin. * Defer the lease_direct mechanism and RDMA core changes to a later patch series. * EXT4 support is in the works and will be rebased on Jan's MAP_SYNC patches. [1]: https://lists.01.org/pipermail/linux-nvdimm/2017-October/012772.html --- MAP_DIRECT is a mechanism that allows an application to establish a mapping where the kernel will not change the block-map, or otherwise dirty the block-map metadata of a file without notification. It supports a "flush from userspace" model where persistent memory applications can bypass the overhead of ongoing coordination of writes with the filesystem, and it provides safety to RDMA operations involving DAX mappings. The kernel always has the ability to revoke access and convert the file back to normal operation after performing a "lease break". Similar to fcntl leases, there is no way for userspace to to cancel the lease break process once it has started, it can only delay it via the /proc/sys/fs/lease-break-time setting. MAP_DIRECT enables XFS to supplant the device-dax interface for mmap-write access to persistent memory with no ongoing coordination with the filesystem via fsync/msync syscalls. The MAP_DIRECT mechanism is complimentary to MAP_SYNC. Here are some scenarios where you would choose one over the other: * 3rd party DMA / RDMA to DAX with hardware that does not support on-demand paging (shared virtual memory) => MAP_DIRECT * Support for reflinked inodes, fallocate-punch-hole, truncate, or any other operation that mutates the block map of an actively mapped file => MAP_SYNC * Userpsace flush => MAP_SYNC or MAP_DIRECT * Assurances that the file's block map metadata is stable, i.e. minimize worst case fault latency by locking out updates => MAP_DIRECT --- Dan Williams (6): mm: introduce MAP_SHARED_VALIDATE, a mechanism to safely define new mmap flags fs, mm: pass fd to ->mmap_validate() fs: MAP_DIRECT core xfs: prepare xfs_break_layouts() for reuse with MAP_DIRECT fs, xfs, iomap: introduce break_layout_nowait() xfs: wire up MAP_DIRECT arch/alpha/include/uapi/asm/mman.h | 1 arch/mips/include/uapi/asm/mman.h | 1 arch/mips/kernel/vdso.c | 2 arch/parisc/include/uapi/asm/mman.h | 1 arch/tile/mm/elf.c | 3 arch/x86/mm/mpx.c | 3 arch/xtensa/include/uapi/asm/mman.h | 1 fs/Kconfig | 1 fs/Makefile | 2 fs/aio.c | 2 fs/mapdirect.c | 237 ++++++++++++++++++++++++++ fs/xfs/Kconfig | 4 fs/xfs/Makefile | 1 fs/xfs/xfs_file.c | 108 ++++++++++++ fs/xfs/xfs_ioctl.c | 1 fs/xfs/xfs_iomap.c | 3 fs/xfs/xfs_iops.c | 1 fs/xfs/xfs_layout.c | 45 +++++ fs/xfs/xfs_layout.h | 13 + fs/xfs/xfs_pnfs.c | 31 --- fs/xfs/xfs_pnfs.h | 8 - include/linux/fs.h | 11 + include/linux/mapdirect.h | 40 ++++ include/linux/mm.h | 9 + include/linux/mman.h | 42 +++++ include/uapi/asm-generic/mman-common.h | 1 include/uapi/asm-generic/mman.h | 1 ipc/shm.c | 3 mm/internal.h | 2 mm/mmap.c | 28 ++- mm/nommu.c | 5 - mm/util.c | 7 - tools/include/uapi/asm-generic/mman-common.h | 1 33 files changed, 557 insertions(+), 62 deletions(-) create mode 100644 fs/mapdirect.c create mode 100644 fs/xfs/xfs_layout.c create mode 100644 fs/xfs/xfs_layout.h create mode 100644 include/linux/mapdirect.h -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
