linux-kernel - Re: [PATCH v11 6/8] mm: Introduce mf_dax_kill

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Date:   Tue, 29 Mar 2022 22:51:38 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        nvdimm@...ts.linux.dev, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, djwong@...nel.org,
        dan.j.williams@...el.com, david@...morbit.com, hch@...radead.org,
        jane.chu@...cle.com
Subject: Re: [PATCH v11 6/8] mm: Introduce mf_dax_kill_procs() for fsdax case

On Sun, Feb 27, 2022 at 08:07:45PM +0800, Shiyang Ruan wrote:
> This function is called at the end of RMAP routine, i.e. filesystem
> recovery function, to collect and kill processes using a shared page of
> DAX file.

I think just throwing RMAP inhere is rather confusing.

> The difference with mf_generic_kill_procs() is, it accepts
> file's (mapping,offset) instead of struct page because different files'
> mappings and offsets may share the same page in fsdax mode.
> It will be called when filesystem's RMAP results are found.

So maybe I'd word the whole log as something like:

This new function is a variant of mf_generic_kill_procs that accepts
a file, offset pair instead o a struct to support multiple files sharing
a DAX mapping.  It is intended to be called by the file systems as
part of the memory_failure handler after the file system performed
a reverse mapping from the storage address to the file and file offset.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@....de>

> index 9b1d56c5c224..0420189e4788 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3195,6 +3195,10 @@ enum mf_flags {
>  	MF_SOFT_OFFLINE = 1 << 3,
>  	MF_UNPOISON = 1 << 4,
>  };
> +#if IS_ENABLED(CONFIG_FS_DAX)
> +int mf_dax_kill_procs(struct address_space *mapping, pgoff_t index,
> +		      unsigned long count, int mf_flags);
> +#endif /* CONFIG_FS_DAX */

No need for the ifdef here, having the stable declaration around is
just fine.

> +#if IS_ENABLED(CONFIG_FS_DAX)

No need for the IS_ENABLED as CONFIG_FS_DAX can't be modular.
A good old #ifdef will do it.

Otherwise looks good:

Reviewed-by: Christoph Hellwig <hch@....de>