Re: [PATCH v3 01/11] pagemap: Introduce ->memory_failure()

[Dan Williams]

On Mon, Feb 8, 2021 at 2:55 AM Shiyang Ruan <ruansy.fnst@xxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxx>
> ---
>  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.