linux-kernel - Re: [PATCH 0/3] dax: clear poison on the fly along pwrite

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Message-ID: <CAPcyv4j8ro5rQKwbwknH+KTcc_8pGDsL8QwmJyi8fDUZE+G8JA@mail.gmail.com>
Date:   Thu, 23 Sep 2021 14:42:10 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jane Chu <jane.chu@...cle.com>
Cc:     "Darrick J. Wong" <djwong@...nel.org>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        "Weiny, Ira" <ira.weiny@...el.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Linux NVDIMM <nvdimm@...ts.linux.dev>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 0/3] dax: clear poison on the fly along pwrite

On Thu, Sep 23, 2021 at 1:56 PM Jane Chu <jane.chu@...cle.com> 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.