linux-kernel - Re: [PATCH v3 01/11] pagemap: Introduce ->memory

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Date:   Wed, 24 Mar 2021 18:39:35 +0100
From:   Christoph Hellwig <hch@....de>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Christoph Hellwig <hch@....de>,
        "ruansy.fnst@...itsu.com" <ruansy.fnst@...itsu.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        device-mapper development <dm-devel@...hat.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        david <david@...morbit.com>, Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Goldwyn Rodrigues <rgoldwyn@...e.de>,
        "qi.fuli@...itsu.com" <qi.fuli@...itsu.com>,
        "y-goto@...itsu.com" <y-goto@...itsu.com>
Subject: Re: [PATCH v3 01/11] pagemap: Introduce ->memory_failure()

On Wed, Mar 24, 2021 at 09:37:01AM -0700, Dan Williams wrote:
> > Eww.  As I said I think the right way is that the file system (or
> > other consumer) can register a set of callbacks for opening the device.
> 
> How does that solve the problem of the driver being notified of all
> pfn failure events?

Ok, I probably just showed I need to spend more time looking at
your proposal vs the actual code..

Don't we have a proper way how one of the nvdimm layers own a
spefific memory range and call directly into that instead of through
a notifier?

> Today pmem only finds out about the ones that are
> notified via native x86 machine check error handling via a notifier
> (yes "firmware-first" error handling fails to do the right thing for
> the pmem driver),

Did any kind of firmware-first error handling ever get anything
right?  I wish people would have learned that by now.

> or the ones that are eventually reported via address
> range scrub, but only for the nvdimms that implement range scrubbing.
> memory_failure() seems a reasonable catch all point to route pfn
> failure events, in an arch independent way, to interested drivers.

Yeah.

> I'm fine swapping out dax_device blocking_notiier chains for your
> proposal, but that does not address all the proposed reworks in my
> list which are:
> 
> - delete "drivers/acpi/nfit/mce.c"
> 
> - teach memory_failure() to be able to communicate range failure
> 
> - enable memory_failure() to defer to a filesystem that can say
> "critical metadata is impacted, no point in trying to do file-by-file
> isolation, bring the whole fs down".

This all sounds sensible.