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To: Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH v5 2/8] drivers/pmem: Allow pmem_clear_poison() to accept
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On Thu, Feb 27, 2020 at 07:28:41PM -0800, Dan Williams wrote:
> "don't perform generic memory-error-handling, there's an fs that owns
> this daxdev and wants to disposition errors". The fs/dax.c
> infrastructure that sets up ->index and ->mapping would still need to
> be there for ext4 until its ready to take on the same responsibility.
> Last I checked the ext4 reverse mapping implementation was not as
> capable as XFS. This goes back to why the initial design avoided
> relying on not universally available / stable reverse-mapping
> facilities and opted for extending the generic mm/memory-failure.c
> implementation.

The important but is that we stop using ->index and ->mapping when XFS
is used as that enables using DAX+reflinks, which actually is the most
requested DAX feature on XFS (way more than silly runtime flag switches
for example).
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Date:   Fri, 28 Feb 2020 06:05:08 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     Dave Chinner <david@fromorbit.com>,
        Vivek Goyal <vgoyal@redhat.com>,
        Jeff Moyer <jmoyer@redhat.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-nvdimm <linux-nvdimm@lists.01.org>,
        Christoph Hellwig <hch@infradead.org>,
        device-mapper development <dm-devel@redhat.com>
Subject: Re: [PATCH v5 2/8] drivers/pmem: Allow pmem_clear_poison() to accept
 arbitrary offset and len
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References: <x49lfoxj622.fsf@segfault.boston.devel.redhat.com>
 <20200220215707.GC10816@redhat.com>
 <x498skv3i5r.fsf@segfault.boston.devel.redhat.com>
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On Thu, Feb 27, 2020 at 07:28:41PM -0800, Dan Williams wrote:
> "don't perform generic memory-error-handling, there's an fs that owns
> this daxdev and wants to disposition errors". The fs/dax.c
> infrastructure that sets up ->index and ->mapping would still need to
> be there for ext4 until its ready to take on the same responsibility.
> Last I checked the ext4 reverse mapping implementation was not as
> capable as XFS. This goes back to why the initial design avoided
> relying on not universally available / stable reverse-mapping
> facilities and opted for extending the generic mm/memory-failure.c
> implementation.

The important but is that we stop using ->index and ->mapping when XFS
is used as that enables using DAX+reflinks, which actually is the most
requested DAX feature on XFS (way more than silly runtime flag switches
for example).