On 2018/12/5 下午8:28, Goldwyn Rodrigues wrote: > This is a support for DAX in btrfs. I understand there have been > previous attempts at it. However, I wanted to make sure copy-on-write > (COW) works on dax as well. > > Before I present this to the FS folks I wanted to run this through the > btrfs. Even though I wish, I cannot get it correct the first time > around :/.. Here are some questions for which I need suggestions: > > Questions: > 1. I have been unable to do checksumming for DAX devices. While > checksumming can be done for reads and writes, it is a problem when mmap > is involved because btrfs kernel module does not get back control after > an mmap() writes. Any ideas are appreciated, or we would have to set > nodatasum when dax is enabled.
I'm not familar with DAX, so it's completely possible I'm talking like an idiot. If btrfs_page_mkwrite() can't provide enough control, then I have a crazy idea. Forcing page fault for every mmap() read/write (completely disable page cache like DIO). So that we could get some control since we're informed to read the page and do some hacks there. Thanks, Qu > > 2. Currently, a user can continue writing on "old" extents of an mmaped file > after a snapshot has been created. How can we enforce writes to be directed > to new extents after snapshots have been created? Do we keep a list of > all mmap()s, and re-mmap them after a snapshot? > > Tested by creating a pmem device in RAM with "memmap=2G!4G" kernel > command line parameter. > > > [PATCH 01/10] btrfs: create a mount option for dax > [PATCH 02/10] btrfs: basic dax read > [PATCH 03/10] btrfs: dax: read zeros from holes > [PATCH 04/10] Rename __endio_write_update_ordered() to > [PATCH 05/10] btrfs: Carve out btrfs_get_extent_map_write() out of > [PATCH 06/10] btrfs: dax write support > [PATCH 07/10] dax: export functions for use with btrfs > [PATCH 08/10] btrfs: dax add read mmap path > [PATCH 09/10] btrfs: dax support for cow_page/mmap_private and shared > [PATCH 10/10] btrfs: dax mmap write > > fs/btrfs/Makefile | 1 > fs/btrfs/ctree.h | 17 ++ > fs/btrfs/dax.c | 303 > ++++++++++++++++++++++++++++++++++++++++++++++++++-- > fs/btrfs/file.c | 29 ++++ > fs/btrfs/inode.c | 54 +++++---- > fs/btrfs/ioctl.c | 5 > fs/btrfs/super.c | 15 ++ > fs/dax.c | 35 ++++-- > include/linux/dax.h | 16 ++ > 9 files changed, 430 insertions(+), 45 deletions(-) > >
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