On Sun, Jun 18, 2017 at 1:18 AM, Christoph Hellwig <hch@xxxxxx> wrote: > On Sat, Jun 17, 2017 at 08:15:05PM -0700, Dan Williams wrote: >> The hang up is that it requires per-fs enabling as it needs to be >> careful to manage mmap_sem vs fs journal locks for example. I know the >> in-development NOVA [1] filesystem is planning to support this out of >> the gate. ext4 would be open to implementing it, but I think xfs is >> cold on the idea. Christoph originally proposed it here [2], before >> Dave went on to propose immutable semantics. >> >> [1]: https://github.com/NVSL/NOVA >> [2]: https://lists.01.org/pipermail/linux-nvdimm/2016-February/004609.html > > And I stand to that statement. Let's get DAX stable first, and > properly cleaned up (e.g. follow on work with separating it entirely > from the block device). Then think hard about how most of the > persistent memory technologies actually work, including the point that > for a lot of workloads page cache will be required at least on the > write side. And then come up with actual real use cases and we can > look into it. I see it differently. We're already at a good point in time to start iterating on a fix for this issue. Ross and Jan have done a lot of good work on the dax stability front, and the block-device separation of dax is well underway. > And stop trying to shoe-horn crap like this in. The kernel shoe-horning all pmem+filesystem-dax applications into abiding page-cache semantics is a problem, and this RFC has already helped move the needle on a couple fronts. 1/ Swapfiles are subtly broken which is something worth fixing, and if it gets us a synchronous-dax mode without major filesystem surgery then that's all for the better. 2/ There's an appetite for just fixing this incrementally in each filesystem's fault handler, so if ext4 was able to prove out an interface / implementation for synchronous faults we could go with that instead of a pre-allocated + immutable interface and let other filesystems set their own timelines. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
