Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20210914233132.3680546-1-jane.chu@oracle.com> <CAPcyv4h3KpOKgy_Cwi5fNBZmR=n1hB33mVzA3fqOY7c3G+GrMA@mail.gmail.com>
 <516ecedc-38b9-1ae3-a784-289a30e5f6df@oracle.com> <20210915161510.GA34830@magnolia>
 <324444b0-6121-d14c-a59f-7689bb206f58@oracle.com>
In-Reply-To: <324444b0-6121-d14c-a59f-7689bb206f58@oracle.com>
From:   Dan Williams <dan.j.williams@intel.com>
Date:   Thu, 23 Sep 2021 14:42:10 -0700
Message-ID: <CAPcyv4j8ro5rQKwbwknH+KTcc_8pGDsL8QwmJyi8fDUZE+G8JA@mail.gmail.com>
Subject: Re: [PATCH 0/3] dax: clear poison on the fly along pwrite
To:     Jane Chu <jane.chu@oracle.com>
Cc:     "Darrick J. Wong" <djwong@kernel.org>,
        Vishal L Verma <vishal.l.verma@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        "Weiny, Ira" <ira.weiny@intel.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Matthew Wilcox <willy@infradead.org>, Jan Kara <jack@suse.cz>,
        Linux NVDIMM <nvdimm@lists.linux.dev>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

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