Re: [f2fs-dev] [PATCH 1/5 v2] f2fs: add mount option for segment allocation policy

[Chao Yu <chao@kernel.org>]

On 2018/2/28 13:09, Jaegeuk Kim wrote:
> Change log from v1:
>  - add doc :)
> 
> This patch adds an mount option, "alloc_mode=%s" having two options, "default"
> and "reuse".
> 
> In "alloc_mode=reuse" case, f2fs starts to allocate segments from 0'th segment
> all the time to reassign segments. It'd be useful for small-sized eMMC parts.

We have to restore old alloc_mode if we encounter any failure in ->remount, right?

Thanks,

> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> ---
>  Documentation/filesystems/f2fs.txt |  2 ++
>  fs/f2fs/f2fs.h                     |  8 ++++++++
>  fs/f2fs/segment.c                  |  5 +++++
>  fs/f2fs/super.c                    | 24 ++++++++++++++++++++++++
>  4 files changed, 39 insertions(+)
> 
> diff --git a/Documentation/filesystems/f2fs.txt b/Documentation/filesystems/f2fs.txt
> index 0caf7da0a532..0409c47584ea 100644
> --- a/Documentation/filesystems/f2fs.txt
> +++ b/Documentation/filesystems/f2fs.txt
> @@ -180,6 +180,8 @@ whint_mode=%s          Control which write hints are passed down to block
>                         down hints. In "user-based" mode, f2fs tries to pass
>                         down hints given by users. And in "fs-based" mode, f2fs
>                         passes down hints with its policy.
> +alloc_mode=%s          Adjust block allocation policy, which supports "reuse"
> +                       and "default".
>  
>  ================================================================================
>  DEBUGFS ENTRIES
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index f68ece08b5a2..d1bfdf691afc 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -1043,6 +1043,11 @@ enum {
>  	WHINT_MODE_FS,		/* pass down hints with F2FS policy */
>  };
>  
> +enum {
> +	ALLOC_MODE_DEFAULT,	/* stay default */
> +	ALLOC_MODE_REUSE,	/* reuse segments as much as possible */
> +};
> +
>  struct f2fs_sb_info {
>  	struct super_block *sb;			/* pointer to VFS super block */
>  	struct proc_dir_entry *s_proc;		/* proc entry */
> @@ -1229,6 +1234,9 @@ struct f2fs_sb_info {
>  #endif
>  	/* For which write hints are passed down to block layer */
>  	int whint_mode;
> +
> +	/* segment allocation policy */
> +	int alloc_mode;
>  };
>  
>  #ifdef CONFIG_F2FS_FAULT_INJECTION
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index 0646d5de8cd0..5e5e2936a26a 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -2170,6 +2170,11 @@ static unsigned int __get_next_segno(struct f2fs_sb_info *sbi, int type)
>  
>  	if (SIT_I(sbi)->last_victim[ALLOC_NEXT])
>  		return SIT_I(sbi)->last_victim[ALLOC_NEXT];
> +
> +	/* find segments from 0 to reuse freed segments */
> +	if (sbi->alloc_mode == ALLOC_MODE_REUSE)
> +		return 0;
> +
>  	return CURSEG_I(sbi, type)->segno;
>  }
>  
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 2d832866720c..1345ef167140 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -130,6 +130,7 @@ enum {
>  	Opt_jqfmt_vfsv0,
>  	Opt_jqfmt_vfsv1,
>  	Opt_whint,
> +	Opt_alloc,
>  	Opt_err,
>  };
>  
> @@ -184,6 +185,7 @@ static match_table_t f2fs_tokens = {
>  	{Opt_jqfmt_vfsv0, "jqfmt=vfsv0"},
>  	{Opt_jqfmt_vfsv1, "jqfmt=vfsv1"},
>  	{Opt_whint, "whint_mode=%s"},
> +	{Opt_alloc, "alloc_mode=%s"},
>  	{Opt_err, NULL},
>  };
>  
> @@ -700,6 +702,23 @@ static int parse_options(struct super_block *sb, char *options)
>  			}
>  			kfree(name);
>  			break;
> +		case Opt_alloc:
> +			name = match_strdup(&args[0]);
> +			if (!name)
> +				return -ENOMEM;
> +
> +			if (strlen(name) == 7 &&
> +					!strncmp(name, "default", 7)) {
> +				sbi->alloc_mode = ALLOC_MODE_DEFAULT;
> +			} else if (strlen(name) == 5 &&
> +					!strncmp(name, "reuse", 5)) {
> +				sbi->alloc_mode = ALLOC_MODE_REUSE;
> +			} else {
> +				kfree(name);
> +				return -EINVAL;
> +			}
> +			kfree(name);
> +			break;
>  		default:
>  			f2fs_msg(sb, KERN_ERR,
>  				"Unrecognized mount option \"%s\" or missing value",
> @@ -1264,6 +1283,10 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
>  	else if (sbi->whint_mode == WHINT_MODE_FS)
>  		seq_printf(seq, ",whint_mode=%s", "fs-based");
>  
> +	if (sbi->alloc_mode == ALLOC_MODE_DEFAULT)
> +		seq_printf(seq, ",alloc_mode=%s", "default");
> +	else if (sbi->alloc_mode == ALLOC_MODE_REUSE)
> +		seq_printf(seq, ",alloc_mode=%s", "reuse");
>  	return 0;
>  }
>  
> @@ -1273,6 +1296,7 @@ static void default_options(struct f2fs_sb_info *sbi)
>  	sbi->active_logs = NR_CURSEG_TYPE;
>  	sbi->inline_xattr_size = DEFAULT_INLINE_XATTR_ADDRS;
>  	sbi->whint_mode = WHINT_MODE_OFF;
> +	sbi->alloc_mode = ALLOC_MODE_DEFAULT;
>  
>  	set_opt(sbi, BG_GC);
>  	set_opt(sbi, INLINE_XATTR);
>