linux-kernel - Re: [f2fs-dev] [PATCH 1/5] f2fs: change default compression algorithm

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Message-ID: <20200310161515.GA1067@sol.localdomain>
Date:   Tue, 10 Mar 2020 09:15:15 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Chao Yu <yuchao0@...wei.com>
Cc:     jaegeuk@...nel.org, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 1/5] f2fs: change default compression algorithm

On Tue, Mar 10, 2020 at 08:50:05PM +0800, Chao Yu wrote:
> Use LZ4 as default compression algorithm, as compared to LZO, it shows
> almost the same compression ratio and much better decompression speed.
> 
> Signed-off-by: Chao Yu <yuchao0@...wei.com>
> ---
>  fs/f2fs/super.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index db3a63f7c769..ebffe7aa08ee 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -1577,7 +1577,7 @@ static void default_options(struct f2fs_sb_info *sbi)
>  	F2FS_OPTION(sbi).test_dummy_encryption = false;
>  	F2FS_OPTION(sbi).s_resuid = make_kuid(&init_user_ns, F2FS_DEF_RESUID);
>  	F2FS_OPTION(sbi).s_resgid = make_kgid(&init_user_ns, F2FS_DEF_RESGID);
> -	F2FS_OPTION(sbi).compress_algorithm = COMPRESS_LZO;
> +	F2FS_OPTION(sbi).compress_algorithm = COMPRESS_LZ4;
>  	F2FS_OPTION(sbi).compress_log_size = MIN_COMPRESS_LOG_SIZE;
>  	F2FS_OPTION(sbi).compress_ext_cnt = 0;
>  	F2FS_OPTION(sbi).bggc_mode = BGGC_MODE_ON;

This makes sense, but it's unclear to me why comparing the different compression
algorithms is happening just now, after support for both LZO and LZ4 was already
merged into mainline and now has to be supported forever.  During review months
ago, multiple people suggested that LZ4 is better than LZO, so there's not much
reason to support LZO at all.

- Eric