On Wed, Jul 26, 2017 at 10:01 AM, Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote: > On Wed, Jul 26, 2017 at 09:53:07AM -0700, Dan Williams wrote: >> It allows for opt-in for applications, or administrators of those >> applications, that know the type of access. > > That's BS. We need to provide the best possible way to access the > media to an application. And whether that's DAX or the page cache > is an implementation detail that should not matter to the application. > > Which doesn't mean there shouldn't be ways to override the default > that the kernel chose based on hardware details, but it's certainly > not something for the application to hardcode, but something for > the adminstrator to decide. Until HMAT came along we had no data in the kernel how to pick a sane default, but we could now very easily make a "if pmem performance < dram, disable dax by default" policy in the kernel. The question for this patch is do we want to add yet another filesystem that adds "-o dax" or require use of per-inode flags to enable dax.
