Re: [RFC PATCH] dax: add badblocks check to Device DAX

On Wed, May 3, 2017 at 9:09 AM, Kani, Toshimitsu <toshi.kani(a)hpe.com&gt; wrote: > On Wed, 2017-05-03 at 08:52 -0700, Dan Williams wrote: > > On Wed, May 3, 2017 at 8:31 AM, Toshi Kani <toshi.kani(a)hpe.com&gt; > > wrote: > > > This is a RFC patch for seeking suggestions.  It adds support > > > of badblocks check in Device DAX by using region-level > > > badblocks list. This patch is only briefly tested. > > > > > > device_dax is a well-isolated self-contained module as it calls > > > alloc_dax() with dev_dax, which is private to device_dax.  For > > > checking badblocks, it needs to call dax_pmem to check with > > > region-level badblocks. > > > > > > This patch attempts to keep device_dax self-contained.  It adds > > > check_error() to dax_operations, and dax_check_error() as a > > > stub with *dev_dax and *dev pointers to convey it to > > > dax_pmem.  I am wondering if this is the right direction, or we > > > should change the modularity to let dax_pmem call alloc_dax() > > > with its dax_pmem (or I completely missed something). > > > > The problem is that device-dax guarantees a given fault > > granularity. To make that guarantee we can't fallback from 1G or > > 2M mappings due to an error. We also can't reasonably go the > > other way and fail mappings that contain a badblock because that > > would change the blast radius of a media error to the fault size. > > Does it mean we expect users to have CPUs with MCE recovery for > Device DAX?  Can we add an attributes like allow error-check & > fall-back? Yes, without MCE recovery device-dax mappings that consume errors will reboot. If an application needs the kernel protection it should be using filesystem-dax.