linux-kernel - Re: [PATCH v3 01/11] pagemap: Introduce ->memory

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Date:   Sat, 6 Mar 2021 12:36:39 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Shiyang Ruan <ruansy.fnst@...fujitsu.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        device-mapper development <dm-devel@...hat.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        david <david@...morbit.com>, Christoph Hellwig <hch@....de>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Goldwyn Rodrigues <rgoldwyn@...e.de>, qi.fuli@...itsu.com,
        Yasunori Goto <y-goto@...itsu.com>
Subject: Re: [PATCH v3 01/11] pagemap: Introduce ->memory_failure()

On Mon, Feb 8, 2021 at 2:55 AM Shiyang Ruan <ruansy.fnst@...fujitsu.com> wrote:
>
> When memory-failure occurs, we call this function which is implemented
> by each kind of devices.  For the fsdax case, pmem device driver
> implements it.  Pmem device driver will find out the block device where
> the error page locates in, and try to get the filesystem on this block
> device.  And finally call filesystem handler to deal with the error.
> The filesystem will try to recover the corrupted data if possiable.
>
> Signed-off-by: Shiyang Ruan <ruansy.fnst@...fujitsu.com>
> ---
>  include/linux/memremap.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 79c49e7f5c30..0bcf2b1e20bd 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -87,6 +87,14 @@ struct dev_pagemap_ops {
>          * the page back to a CPU accessible page.
>          */
>         vm_fault_t (*migrate_to_ram)(struct vm_fault *vmf);
> +
> +       /*
> +        * Handle the memory failure happens on one page.  Notify the processes
> +        * who are using this page, and try to recover the data on this page
> +        * if necessary.
> +        */
> +       int (*memory_failure)(struct dev_pagemap *pgmap, unsigned long pfn,
> +                             int flags);
>  };

After the conversation with Dave I don't see the point of this. If
there is a memory_failure() on a page, why not just call
memory_failure()? That already knows how to find the inode and the
filesystem can be notified from there.

Although memory_failure() is inefficient for large range failures, I'm
not seeing a better option, so I'm going to test calling
memory_failure() over a large range whenever an in-use dax-device is
hot-removed.