On 12/07/2016 04:45 PM, Liu Bo wrote:
This has implemented DAX support for btrfs with nocow and single-device. DAX is developed for block devices that are memory-like in order to avoid double buffer in both page cache and the storage, so DAX can performs reads and writes directly to the storage device, and for those who prefer to using filesystem, filesystem dax support can help to map the storage into userspace for file-mapping. Since I haven't figure out how to map multiple devices to userspace without pagecache, this DAX support is only for single-device, and I don't think DAX(Direct Access) can work with cow, this is limited to nocow case. I made this by setting nodatacow in dax mount option.
Interesting, this is a nice small start. It might make more sense to limit snapshots to readonly in DAX mode until we can figure out how to cow properly. I think it can be done, I just need to sit down with the dax code to do a good review.
But bigger picture, if we can't cow and we can't crc and we can't multi-device, I'd rather let XFS/ext4 sort out the dax space until we pull in more of the btrfs features too.
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