linux-kernel - Re: [GIT PULL] device-dax for 5.1: PMEM as RAM

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Message-ID: <CAHk-=wgnJd_qY1wGc0KcoGrNz3Mp9-8mQFMDLoTXvEMVtAxyZQ@mail.gmail.com>
Date:   Mon, 11 Mar 2019 17:07:43 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux MM <linux-mm@...ck.org>,
        Dave Hansen <dave.hansen@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>
Subject: Re: [GIT PULL] device-dax for 5.1: PMEM as RAM

On Mon, Mar 11, 2019 at 8:37 AM Dan Williams <dan.j.williams@...el.com> wrote:
>
> Another feature the userspace tooling can support for the PMEM as RAM
> case is the ability to complete an Address Range Scrub of the range
> before it is added to the core-mm. I.e at least ensure that previously
> encountered poison is eliminated.

Ok, so this at least makes sense as an argument to me.

In the "PMEM as filesystem" part, the errors have long-term history,
while in "PMEM as RAM" the memory may be physically the same thing,
but it doesn't have the history and as such may not be prone to
long-term errors the same way.

So that validly argues that yes, when used as RAM, the likelihood for
errors is much lower because they don't accumulate the same way.

> The driver can also publish an
> attribute to indicate when rep; mov is recoverable, and gate the
> hotplug policy on the result. In my opinion a positive indicator of
> the cpu's ability to recover rep; mov exceptions is a gap that needs
> addressing.

Is there some way to say "don't raise MC for this region"? Or at least
limit it to a nonfatal one?

                 Linus