Re: [PATCH 5/5] dax: "Hotplug" persistent memory for use like normal RAM

[Dan Williams]

On Thu, Jan 24, 2019 at 10:13 PM Jane Chu <jane.chu@xxxxxxxxxx> wrote:
>
> Hi, Dave,
>
> While chatting with my colleague Erwin about the patchset, it occurred
> that we're not clear about the error handling part. Specifically,
>
> 1. If an uncorrectable error is detected during a 'load' in the hot
> plugged pmem region, how will the error be handled?  will it be
> handled like PMEM or DRAM?

DRAM.

> 2. If a poison is set, and is persistent, which entity should clear
> the poison, and badblock(if applicable)? If it's user's responsibility,
> does ndctl support the clearing in this mode?

With persistent memory advertised via a static logical-to-physical
storage/dax device mapping, once an error develops it destroys a
physical *and* logical part of a device address space. That loss of
logical address space makes error clearing a necessity. However, with
the DRAM / "System RAM" error handling model, the OS can just offline
the page and map a different one to repair the logical address space.
So, no, ndctl will not have explicit enabling to clear volatile
errors, the OS will just dynamically offline problematic pages.