Re: [PATCH v12 00/20] DAX: Page cache bypass for filesystems on memory storage
From: Christoph Hellwig
Date: Wed Dec 10 2014 - 09:03:57 EST
What is the status of this patch set?
On Fri, Oct 24, 2014 at 05:20:32PM -0400, Matthew Wilcox wrote:
> DAX is a replacement for the variation of XIP currently supported by
> the ext2 filesystem. We have three different things in the tree called
> 'XIP', and the new focus is on access to data rather than executables,
> so a name change was in order. DAX stands for Direct Access. The X is
> for eXciting.
> The new focus on data access has resulted in more careful attention to
> races that exist in the current XIP code, but are not hit by the use-case
> that it was designed for. XIP's architecture worked fine for ext2, but
> DAX is architected to work with modern filsystems such as ext4 and XFS.
> DAX is not intended for use with btrfs; the value that btrfs adds relies
> on manipulating data and writing data to different locations, while DAX's
> value is for write-in-place and keeping the kernel from touching the data.
> DAX was developed in order to support NV-DIMMs, but it's become clear that
> its usefuless extends beyond NV-DIMMs and there are several potential
> customers including the tracing machinery. Other people want to place
> the kernel log in an area of memory, as long as they have a BIOS that
> does not clear DRAM on reboot.
> Patch 1 is a bug fix. It is obviously correct, and should be included
> into 3.18.
> Patch 2 starts the transformation by changing how ->direct_access works.
> Much code is moved from the drivers and filesystems into the block layer,
> and we add the flexibility of being able to map more than one page at
> a time. It would be good to get this patch into 3.18 as it is also
> useful for people who are pursuing non-DAX approaches to working with
> persistent memory.
> Patch 3 is also a bug fix, probably worth including in 3.18.
> Patches 4 & 5 are infrastructure for DAX.
> Patches 6-10 replace the XIP code with its DAX equivalents, transforming
> ext2 to use the DAX code as we go. Note that patch 10 is the
> Documentation patch.
> Patches 11-17 clean up after the XIP code, removing the infrastructure
> that is no longer needed and renaming various XIP things to DAX.
> Most of these patches were added after Jan found things he didn't
> like in an earlier version of the ext4 patch ... that had been copied
> from ext2. So ext2 i being transformed to do things the same way that
> ext4 will later. The ability to mount ext2 filesystems with the 'xip'
> option is retained, although the 'dax' option is now preferred.
> Patch 18 adds some DAX infrastructure to support ext4.
> Patch 19 adds DAX support to ext4. It is broadly similar to ext2's DAX
> support, but it is more efficient than ext4's due to its support for
> unwritten extents.
> Patch 20 is another cleanup patch renaming XIP to DAX.
> My thanks to Mathieu Desnoyers for his reviews of the v11 patchset. Most
> of the changes below were based on his feedback.
> Changes since v11:
> - Rebased to 3.18-rc1, dropping patch "vfs: Add copy_to_iter(),
> copy_from_iter() and iov_iter_zero()" as it was merged through Al's tree.
> - Added cc to stable@xxxxxxxxxxxxxxx on patch 1
> - Fixed comment style in brd.c (Mathieu)
> - Make more functions in fs.h common with and without CONFIG_FS_DAX set
> - Improve type-checking with !CONFIG_FS_DAX
> - Simplify check for holes in dax_io()
> - Harden the loop in dax_clear_blocks()
> - Add missing check against truncate of a page covering a hole
> - Fix the page-fault handler to work for block devices too
> - Change a few more places that mentioned 'XIP' into 'DAX'
> - Update DAX documentation in a couple of places
> Matthew Wilcox (19):
> axonram: Fix bug in direct_access
> block: Change direct_access calling convention
> mm: Fix XIP fault vs truncate race
> mm: Allow page fault handlers to perform the COW
> vfs,ext2: Introduce IS_DAX(inode)
> dax,ext2: Replace XIP read and write with DAX I/O
> dax,ext2: Replace ext2_clear_xip_target with dax_clear_blocks
> dax,ext2: Replace the XIP page fault handler with the DAX page fault
> dax,ext2: Replace xip_truncate_page with dax_truncate_page
> dax: Replace XIP documentation with DAX documentation
> vfs: Remove get_xip_mem
> ext2: Remove ext2_xip_verify_sb()
> ext2: Remove ext2_use_xip
> ext2: Remove xip.c and xip.h
> vfs,ext2: Remove CONFIG_EXT2_FS_XIP and rename CONFIG_FS_XIP to
> ext2: Remove ext2_aops_xip
> ext2: Get rid of most mentions of XIP in ext2
> dax: Add dax_zero_page_range
> brd: Rename XIP to DAX
> Ross Zwisler (1):
> ext4: Add DAX functionality
> Documentation/filesystems/00-INDEX | 5 +-
> Documentation/filesystems/Locking | 3 -
> Documentation/filesystems/dax.txt | 91 +++++++
> Documentation/filesystems/ext2.txt | 5 +-
> Documentation/filesystems/ext4.txt | 4 +
> Documentation/filesystems/vfs.txt | 7 -
> Documentation/filesystems/xip.txt | 68 -----
> MAINTAINERS | 6 +
> arch/powerpc/sysdev/axonram.c | 19 +-
> drivers/block/Kconfig | 13 +-
> drivers/block/brd.c | 28 +-
> drivers/s390/block/dcssblk.c | 21 +-
> fs/Kconfig | 21 +-
> fs/Makefile | 1 +
> fs/block_dev.c | 40 +++
> fs/dax.c | 530 +++++++++++++++++++++++++++++++++++++
> fs/exofs/inode.c | 1 -
> fs/ext2/Kconfig | 11 -
> fs/ext2/Makefile | 1 -
> fs/ext2/ext2.h | 10 +-
> fs/ext2/file.c | 45 +++-
> fs/ext2/inode.c | 38 +--
> fs/ext2/namei.c | 13 +-
> fs/ext2/super.c | 53 ++--
> fs/ext2/xip.c | 91 -------
> fs/ext2/xip.h | 26 --
> fs/ext4/ext4.h | 6 +
> fs/ext4/file.c | 50 +++-
> fs/ext4/indirect.c | 18 +-
> fs/ext4/inode.c | 89 +++++--
> fs/ext4/namei.c | 10 +-
> fs/ext4/super.c | 39 ++-
> fs/open.c | 5 +-
> include/linux/blkdev.h | 6 +-
> include/linux/fs.h | 34 +--
> include/linux/mm.h | 1 +
> include/linux/rmap.h | 2 +-
> mm/Makefile | 1 -
> mm/fadvise.c | 6 +-
> mm/filemap.c | 25 +-
> mm/filemap_xip.c | 483 ---------------------------------
> mm/madvise.c | 2 +-
> mm/memory.c | 33 ++-
> scripts/diffconfig | 1 -
> 44 files changed, 1069 insertions(+), 893 deletions(-)
> create mode 100644 Documentation/filesystems/dax.txt
> delete mode 100644 Documentation/filesystems/xip.txt
> create mode 100644 fs/dax.c
> delete mode 100644 fs/ext2/xip.c
> delete mode 100644 fs/ext2/xip.h
> delete mode 100644 mm/filemap_xip.c
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