[PATCH v2 00/10] evacuate struct page from the block layer, introduce __pfn_t

From: Dan Williams
Date: Wed May 06 2015 - 16:07:42 EST

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Changes since v1 [1]:

1/ added include/asm-generic/pfn.h for the __pfn_t definition and helpers.

2/ added kmap_atomic_pfn_t()

3/ rebased on v4.1-rc2

[1]: http://marc.info/?l=linux-kernel&m=142653770511970&w=2

---

A lead in note, this looks scarier than it is. Most of the code thrash
is automated via Coccinelle. Also the subtle differences behind an
'unsigned long pfn' and a '__pfn_t' are mitigated by type-safety and a
Kconfig option (default disabled CONFIG_PMEM_IO) that globally controls
whether a pfn and a __pfn_t are equivalent.

The motivation for this change is persistent memory and the desire to
use it not only via the pmem driver, but also as a memory target for I/O
(DAX, O_DIRECT, DMA, RDMA, etc) in other parts of the kernel. Aside
from the pmem driver and DAX, persistent memory is not able to be used
in these I/O scenarios due to the lack of a backing struct page, i.e.
persistent memory is not part of the memmap. This patchset takes the
position that the solution is to teach I/O paths that want to operate on
persistent memory to do so by referencing a __pfn_t. The alternatives
are discussed in the changelog for "[PATCH v2 01/10] arch: introduce
__pfn_t for persistent memory i/o", copied here:

Alternatives:

1/ Provide struct page coverage for persistent memory in
DRAM. The expectation is that persistent memory capacities make
this untenable in the long term.

2/ Provide struct page coverage for persistent memory with
persistent memory. While persistent memory may have near DRAM
performance characteristics it may not have the same
write-endurance of DRAM. Given the update frequency of struct
page objects it may not be suitable for persistent memory.

3/ Dynamically allocate struct page. This appears to be on
the order of the complexity of converting code paths to use
__pfn_t references instead of struct page, and the amount of
setup required to establish a valid struct page reference is
mostly wasted when the only usage in the block stack is to
perform a page_to_pfn() conversion for dma-mapping. Instances
of kmap() / kmap_atomic() usage appear to be the only occasions
in the block stack where struct page is non-trivially used. A
new kmap_atomic_pfn_t() is proposed to handle those cases.

---

Dan Williams (9):
arch: introduce __pfn_t for persistent memory i/o
block: add helpers for accessing a bio_vec page
block: convert .bv_page to .bv_pfn bio_vec
dma-mapping: allow archs to optionally specify a ->map_pfn() operation
scatterlist: use sg_phys()
x86: support dma_map_pfn()
x86: support kmap_atomic_pfn_t() for persistent memory
dax: convert to __pfn_t
block: base support for pfn i/o

Matthew Wilcox (1):
scatterlist: support "page-less" (__pfn_t only) entries

arch/Kconfig | 6 ++
arch/arm/mm/dma-mapping.c | 2 -
arch/microblaze/kernel/dma.c | 2 -
arch/powerpc/sysdev/axonram.c | 6 +-
arch/x86/Kconfig | 7 ++
arch/x86/kernel/Makefile | 1
arch/x86/kernel/amd_gart_64.c | 22 +++++-
arch/x86/kernel/kmap.c | 95 ++++++++++++++++++++++++++
arch/x86/kernel/pci-nommu.c | 22 +++++-
arch/x86/kernel/pci-swiotlb.c | 4 +
arch/x86/pci/sta2x11-fixup.c | 4 +
arch/x86/xen/pci-swiotlb-xen.c | 4 +
block/bio-integrity.c | 8 +-
block/bio.c | 82 ++++++++++++++++------
block/blk-core.c | 13 +++-
block/blk-integrity.c | 7 +-
block/blk-lib.c | 2 -
block/blk-merge.c | 15 ++--
block/bounce.c | 26 ++++---
drivers/block/aoe/aoecmd.c | 8 +-
drivers/block/brd.c | 6 +-
drivers/block/drbd/drbd_bitmap.c | 5 +
drivers/block/drbd/drbd_main.c | 6 +-
drivers/block/drbd/drbd_receiver.c | 4 +
drivers/block/drbd/drbd_worker.c | 3 +
drivers/block/floppy.c | 6 +-
drivers/block/loop.c | 13 ++--
drivers/block/nbd.c | 8 +-
drivers/block/nvme-core.c | 2 -
drivers/block/pktcdvd.c | 11 ++-
drivers/block/pmem.c | 16 +++-
drivers/block/ps3disk.c | 2 -
drivers/block/ps3vram.c | 2 -
drivers/block/rbd.c | 2 -
drivers/block/rsxx/dma.c | 2 -
drivers/block/umem.c | 2 -
drivers/block/zram/zram_drv.c | 10 +--
drivers/dma/ste_dma40.c | 5 -
drivers/iommu/amd_iommu.c | 21 ++++--
drivers/iommu/intel-iommu.c | 26 +++++--
drivers/iommu/iommu.c | 2 -
drivers/md/bcache/btree.c | 4 +
drivers/md/bcache/debug.c | 6 +-
drivers/md/bcache/movinggc.c | 2 -
drivers/md/bcache/request.c | 6 +-
drivers/md/bcache/super.c | 10 +--
drivers/md/bcache/util.c | 5 +
drivers/md/bcache/writeback.c | 2 -
drivers/md/dm-crypt.c | 12 ++-
drivers/md/dm-io.c | 2 -
drivers/md/dm-log-writes.c | 14 ++--
drivers/md/dm-verity.c | 2 -
drivers/md/raid1.c | 50 +++++++-------
drivers/md/raid10.c | 38 +++++-----
drivers/md/raid5.c | 6 +-
drivers/mmc/card/queue.c | 4 +
drivers/s390/block/dasd_diag.c | 2 -
drivers/s390/block/dasd_eckd.c | 14 ++--
drivers/s390/block/dasd_fba.c | 6 +-
drivers/s390/block/dcssblk.c | 8 +-
drivers/s390/block/scm_blk.c | 2 -
drivers/s390/block/scm_blk_cluster.c | 2 -
drivers/s390/block/xpram.c | 2 -
drivers/scsi/mpt2sas/mpt2sas_transport.c | 6 +-
drivers/scsi/mpt3sas/mpt3sas_transport.c | 6 +-
drivers/scsi/sd_dif.c | 4 +
drivers/staging/android/ion/ion_chunk_heap.c | 4 +
drivers/staging/lustre/lustre/llite/lloop.c | 2 -
drivers/target/target_core_file.c | 4 +
drivers/xen/biomerge.c | 4 +
drivers/xen/swiotlb-xen.c | 29 +++++---
fs/9p/vfs_addr.c | 2 -
fs/block_dev.c | 2 -
fs/btrfs/check-integrity.c | 6 +-
fs/btrfs/compression.c | 12 ++-
fs/btrfs/disk-io.c | 5 +
fs/btrfs/extent_io.c | 8 +-
fs/btrfs/file-item.c | 8 +-
fs/btrfs/inode.c | 19 +++--
fs/btrfs/raid56.c | 4 +
fs/btrfs/volumes.c | 2 -
fs/buffer.c | 4 +
fs/dax.c | 9 +-
fs/direct-io.c | 2 -
fs/exofs/ore.c | 4 +
fs/exofs/ore_raid.c | 2 -
fs/ext4/page-io.c | 2 -
fs/ext4/readpage.c | 4 +
fs/f2fs/data.c | 4 +
fs/f2fs/segment.c | 2 -
fs/gfs2/lops.c | 4 +
fs/jfs/jfs_logmgr.c | 4 +
fs/logfs/dev_bdev.c | 10 +--
fs/mpage.c | 2 -
fs/splice.c | 2 -
include/asm-generic/dma-mapping-common.h | 30 ++++++++
include/asm-generic/memory_model.h | 1
include/asm-generic/pfn.h | 67 ++++++++++++++++++
include/asm-generic/scatterlist.h | 10 +++
include/crypto/scatterwalk.h | 10 +++
include/linux/bio.h | 24 ++++---
include/linux/blk_types.h | 20 +++++
include/linux/blkdev.h | 6 +-
include/linux/dma-debug.h | 23 +++++-
include/linux/dma-mapping.h | 8 ++
include/linux/highmem.h | 23 ++++++
include/linux/mm.h | 1
include/linux/scatterlist.h | 91 ++++++++++++++++++++++---
include/linux/swiotlb.h | 4 +
init/Kconfig | 13 ++++
kernel/power/block_io.c | 2 -
lib/dma-debug.c | 10 ++-
lib/iov_iter.c | 22 +++---
lib/swiotlb.c | 20 ++++-
mm/page_io.c | 10 +--
net/ceph/messenger.c | 2 -
116 files changed, 896 insertions(+), 372 deletions(-)
create mode 100644 arch/x86/kernel/kmap.c
create mode 100644 include/asm-generic/pfn.h
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Next message: Dan Williams: "[PATCH v2 01/10] arch: introduce __pfn_t for persistent memory i/o"
Previous message: Guenter Roeck: "Re: [PATCH V1 5/6] watchdog: da9062: DA9062 watchdog driver"
Next in thread: Dan Williams: "[PATCH v2 01/10] arch: introduce __pfn_t for persistent memory i/o"
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