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

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Date:   Wed, 24 Mar 2021 08:47:51 +0100
From:   Christoph Hellwig <hch@....de>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     "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>, Christoph Hellwig <hch@....de>,
        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 Tue, Mar 23, 2021 at 07:19:28PM -0700, Dan Williams wrote:
> So I think the path forward is:
> 
> - teach memory_failure() to allow for ranged failures
> 
> - let interested drivers register for memory failure events via a
> blocking_notifier_head

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.
I have a series I need to finish and send out to do that for block
devices.  We probably also need the concept of a holder for the dax
device to make it work nicely, as otherwise we're going to have a bit
of a mess.

> This obviously does not solve Dave's desire to get this type of error
> reporting on block_devices, but I think there's nothing stopping a
> parallel notifier chain from being created for block-devices, but
> that's orthogonal to requirements and capabilities provided by
> dax-devices.

FYI, my series could easily accomodate that if we ever get a block
driver that actually could report such errors.