linux-kernel - Re: [f2fs-dev] [PATCH 1/2] f2fs: add compress

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Date:   Mon, 23 Nov 2020 10:46:47 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     Daeho Jeong <daeho43@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, kernel-team@...roid.com,
        Daeho Jeong <daehojeong@...gle.com>
Subject: Re: [f2fs-dev] [PATCH 1/2] f2fs: add compress_mode mount option

On Mon, Nov 23, 2020 at 12:17:50PM +0900, Daeho Jeong wrote:
> From: Daeho Jeong <daehojeong@...gle.com>
> 
> We will add a new "compress_mode" mount option to control file
> compression mode. This supports "fs-based" and "user-based".
> In "fs-based" mode (default), f2fs does automatic compression on
> the compression enabled files. In "user-based" mode, f2fs disables
> the automaic compression and gives the user discretion of choosing
> the target file and the timing. It means the user can do manual
> compression/decompression on the compression enabled files using ioctls.
> 
> Signed-off-by: Daeho Jeong <daehojeong@...gle.com>
> ---
>  Documentation/filesystems/f2fs.rst |  7 +++++++
>  fs/f2fs/data.c                     | 10 +++++-----
>  fs/f2fs/f2fs.h                     | 30 ++++++++++++++++++++++++++++++
>  fs/f2fs/segment.c                  |  2 +-
>  fs/f2fs/super.c                    | 23 +++++++++++++++++++++++
>  5 files changed, 66 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
> index b8ee761c9922..0679c53d5012 100644
> --- a/Documentation/filesystems/f2fs.rst
> +++ b/Documentation/filesystems/f2fs.rst
> @@ -260,6 +260,13 @@ compress_extension=%s	 Support adding specified extension, so that f2fs can enab
>  			 For other files, we can still enable compression via ioctl.
>  			 Note that, there is one reserved special extension '*', it
>  			 can be set to enable compression for all files.
> +compress_mode=%s	 Control file compression mode. This supports "fs-based" and
> +			 "user-based". In "fs-based" mode (default), f2fs does
> +			 automatic compression on the compression enabled files.
> +			 In "user-based" mode, f2fs disables the automaic compression
> +			 and gives the user discretion of choosing the target file and
> +			 the timing. The user can do manual compression/decompression
> +			 on the compression enabled files using ioctls.

Please clarify in the documentation what it means for compression-enabled files
to not be compressed.  It is not obvious.

- Eric