On Tue, Jun 26, 2018 at 2:23 PM, Kani, Toshi toshi.kani@hpe.com wrote:
On Tue, 2018-06-26 at 14:02 -0700, Dan Williams wrote:
On Tue, Jun 26, 2018 at 1:54 PM, Kani, Toshi toshi.kani@hpe.com wrote:
[..]
When this dm change was made, the pmem driver supported DAX for both raw and memory modes (note: sector mode does not use the pmem driver). I think the issue was introduced when we dropped DAX support from raw mode.
Still DAX with raw mode never really worked any way. It was also something that was broken from day one. So what happens to someone who happened to avoid all the problems with page-less DAX and enabled device-mapper on top? That failure mode detail needs to be added to this changelog if we want to propose this for -stable.
My point is that the behavior should be consistent between pmem and device-mapper. When -o dax succeeds on a pmem, then it should succeed on a device-mapper on top of that pmem.
Has the drop of dax support from raw mode made to -stable back to the baseline accepted 545ed20e6df6? It will introduce inconsistency, otherwise.
That commit, 569d0365f571 "dax: require 'struct page' by default for filesystem dax", has not been tagged for -stable.