linux-kernel - Re: [PATCH v9 06/10] fsdax: Introduce dax_lock_mapping

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Message-ID: <CAPcyv4jVDfpHb1DCW+NLXH2YBgLghCVy8o6wrc02CXx4g-Bv7Q@mail.gmail.com>
Date:   Tue, 4 Jan 2022 14:55:54 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Linux NVDIMM <nvdimm@...ts.linux.dev>,
        Linux MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        "Darrick J. Wong" <djwong@...nel.org>, david <david@...morbit.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jane Chu <jane.chu@...cle.com>, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v9 06/10] fsdax: Introduce dax_lock_mapping_entry()

On Sun, Dec 26, 2021 at 6:35 AM Shiyang Ruan <ruansy.fnst@...itsu.com> wrote:
>
> The current dax_lock_page() locks dax entry by obtaining mapping and
> index in page.  To support 1-to-N RMAP in NVDIMM, we need a new function
> to lock a specific dax entry corresponding to this file's mapping,index.
> And output the page corresponding to the specific dax entry for caller
> use.

Is this necessary? The point of dax_lock_page() is to ensure that the
fs does not destroy the address_space, or remap the pfn while
memory_failure() is operating on the pfn. In the notify_failure case
control is handed to the fs so I expect it can make those guarantees
itself, no?