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Date:   Thu, 23 Sep 2021 14:42:10 -0700
From:   Dan Williams <>
To:     Jane Chu <>
Cc:     "Darrick J. Wong" <>,
        Vishal L Verma <>,
        Dave Jiang <>,
        "Weiny, Ira" <>,
        Al Viro <>,
        Matthew Wilcox <>, Jan Kara <>,
        Linux NVDIMM <>,
        Linux Kernel Mailing List <>,
        linux-fsdevel <>
Subject: Re: [PATCH 0/3] dax: clear poison on the fly along pwrite

On Thu, Sep 23, 2021 at 1:56 PM Jane Chu <> wrote:
> > This (AFAICT) has already been done for dax_zero_page_range, so I sense
> > that Dan is trying to save you a bunch of code plumbing work by nudging
> > you towards doing s/dax_clear_poison/dax_zero_page_range/ to this series
> > and then you only need patches 2-3.
> Thanks Darrick for the explanation!
> I don't mind to add DM layer support, it sounds straight forward.
> I also like your latest patch and am wondering if the clear_poison API
> is still of value.

No, the discussion about fallocate(...ZEROINIT...) has lead to a
better solution. Instead of making error clearing a silent /
opportunistic side-effect of writes, or trying to define new fallocate
mode, just add a new RWF_CLEAR_HWERROR flag to pwritev2(). This allows
for dax_direct_access() to map the page regardless of poison and
trigger pmem_copy_from_iter() to precisely handle sub-page poison.

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