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

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Date:   Tue, 14 Sep 2021 21:44:10 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jane Chu <jane.chu@...cle.com>
Cc:     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 Tue, Sep 14, 2021 at 4:32 PM Jane Chu <jane.chu@...cle.com> wrote:
>
> If pwrite(2) encounters poison in a pmem range, it fails with EIO.
> This is unecessary if hardware is capable of clearing the poison.
>
> Though not all dax backend hardware has the capability of clearing
> poison on the fly, but dax backed by Intel DCPMEM has such capability,
> and it's desirable to, first, speed up repairing by means of it;
> second, maintain backend continuity instead of fragmenting it in
> search for clean blocks.
>
> Jane Chu (3):
>   dax: introduce dax_operation dax_clear_poison

The problem with new dax operations is that they need to be plumbed
not only through fsdax and pmem, but also through device-mapper.

In this case I think we're already covered by dax_zero_page_range().
That will ultimately trigger pmem_clear_poison() and it is routed
through device-mapper properly.

Can you clarify why the existing dax_zero_page_range() is not sufficient?

>   dax: introduce dax_clear_poison to dax pwrite operation
>   libnvdimm/pmem: Provide pmem_dax_clear_poison for dax operation
>
>  drivers/dax/super.c   | 13 +++++++++++++
>  drivers/nvdimm/pmem.c | 17 +++++++++++++++++
>  fs/dax.c              |  9 +++++++++
>  include/linux/dax.h   |  6 ++++++
>  4 files changed, 45 insertions(+)
>
> --
> 2.18.4
>