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Subject: Re: [f2fs-dev] [PATCH v2] f2fs: rename checkpoint=merge mount option
 to checkpoint_merge
To:     Daeho Jeong <daeho43@gmail.com>, <linux-kernel@vger.kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>, <kernel-team@android.com>
CC:     Daeho Jeong <daehojeong@google.com>
References: <20210202051829.2127214-1-daeho43@gmail.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <ef27f0cc-87b6-cea1-31a6-f2837d6a673c@huawei.com>
Date:   Tue, 2 Feb 2021 15:40:30 +0800
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On 2021/2/2 13:18, Daeho Jeong wrote:
> From: Daeho Jeong <daehojeong@google.com>
> 
> As checkpoint=merge comes in, mount option setting related to checkpoint
> had been mixed up and it became hard to understand. So, I separated
> this option from "checkpoint=" and made another mount option
> "checkpoint_merge" for this.
> 
> Signed-off-by: Daeho Jeong <daehojeong@google.com>
> ---
> v2: renamed "checkpoint=merge" to "checkpoint_merge"
> ---
>   Documentation/filesystems/f2fs.rst |  6 +++---
>   fs/f2fs/super.c                    | 26 ++++++++++++++------------
>   2 files changed, 17 insertions(+), 15 deletions(-)
> 
> diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
> index d0ead45dc706..475994ed8b15 100644
> --- a/Documentation/filesystems/f2fs.rst
> +++ b/Documentation/filesystems/f2fs.rst
> @@ -247,9 +247,9 @@ checkpoint=%s[:%u[%]]	 Set to "disable" to turn off checkpointing. Set to "enabl
>   			 hide up to all remaining free space. The actual space that
>   			 would be unusable can be viewed at /sys/fs/f2fs/<disk>/unusable
>   			 This space is reclaimed once checkpoint=enable.
> -			 Here is another option "merge", which creates a kernel daemon
> -			 and makes it to merge concurrent checkpoint requests as much
> -			 as possible to eliminate redundant checkpoint issues. Plus,
> +checkpoint_merge	 When checkpoint is enabled, this can be used to create a kernel
> +			 daemon and make it to merge concurrent checkpoint requests as
> +			 much as possible to eliminate redundant checkpoint issues. Plus,
>   			 we can eliminate the sluggish issue caused by slow checkpoint
>   			 operation when the checkpoint is done in a process context in
>   			 a cgroup having low i/o budget and cpu shares. To make this
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 56696f6cfa86..d8603e6c4916 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -145,6 +145,7 @@ enum {
>   	Opt_checkpoint_disable_cap_perc,
>   	Opt_checkpoint_enable,
>   	Opt_checkpoint_merge,
> +	Opt_nocheckpoint_merge,
>   	Opt_compress_algorithm,
>   	Opt_compress_log_size,
>   	Opt_compress_extension,
> @@ -215,7 +216,8 @@ static match_table_t f2fs_tokens = {
>   	{Opt_checkpoint_disable_cap, "checkpoint=disable:%u"},
>   	{Opt_checkpoint_disable_cap_perc, "checkpoint=disable:%u%%"},
>   	{Opt_checkpoint_enable, "checkpoint=enable"},
> -	{Opt_checkpoint_merge, "checkpoint=merge"},
> +	{Opt_checkpoint_merge, "checkpoint_merge"},
> +	{Opt_nocheckpoint_merge, "nocheckpoint_merge"},
>   	{Opt_compress_algorithm, "compress_algorithm=%s"},
>   	{Opt_compress_log_size, "compress_log_size=%u"},
>   	{Opt_compress_extension, "compress_extension=%s"},
> @@ -946,6 +948,9 @@ static int parse_options(struct super_block *sb, char *options, bool is_remount)
>   		case Opt_checkpoint_merge:
>   			set_opt(sbi, MERGE_CHECKPOINT);
>   			break;
> +		case Opt_nocheckpoint_merge:
> +			clear_opt(sbi, MERGE_CHECKPOINT);
> +			break;
>   #ifdef CONFIG_F2FS_FS_COMPRESSION
>   		case Opt_compress_algorithm:
>   			if (!f2fs_sb_has_compression(sbi)) {
> @@ -1142,12 +1147,6 @@ static int parse_options(struct super_block *sb, char *options, bool is_remount)
>   		return -EINVAL;
>   	}
>   
> -	if (test_opt(sbi, DISABLE_CHECKPOINT) &&
> -			test_opt(sbi, MERGE_CHECKPOINT)) {
> -		f2fs_err(sbi, "checkpoint=merge cannot be used with checkpoint=disable\n");
> -		return -EINVAL;
> -	}
> -
>   	/* Not pass down write hints if the number of active logs is lesser
>   	 * than NR_CURSEG_PERSIST_TYPE.
>   	 */
> @@ -1782,7 +1781,7 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
>   		seq_printf(seq, ",checkpoint=disable:%u",
>   				F2FS_OPTION(sbi).unusable_cap);
>   	if (test_opt(sbi, MERGE_CHECKPOINT))
> -		seq_puts(seq, ",checkpoint=merge");
> +		seq_puts(seq, ",checkpoint_merge");

Other noxxx options will be shown in show_options(), how about following them?

>   	if (F2FS_OPTION(sbi).fsync_mode == FSYNC_MODE_POSIX)
>   		seq_printf(seq, ",fsync_mode=%s", "posix");
>   	else if (F2FS_OPTION(sbi).fsync_mode == FSYNC_MODE_STRICT)
> @@ -1827,6 +1826,7 @@ static void default_options(struct f2fs_sb_info *sbi)
>   	sbi->sb->s_flags |= SB_LAZYTIME;
>   	set_opt(sbi, FLUSH_MERGE);
>   	set_opt(sbi, DISCARD);
> +	clear_opt(sbi, MERGE_CHECKPOINT);

Why should we clear checkpoint_merge option in default_options()?

Thanks,

>   	if (f2fs_sb_has_blkzoned(sbi))
>   		F2FS_OPTION(sbi).fs_mode = FS_MODE_LFS;
>   	else
> @@ -2066,9 +2066,8 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
>   		}
>   	}
>   
> -	if (!test_opt(sbi, MERGE_CHECKPOINT)) {
> -		f2fs_stop_ckpt_thread(sbi);
> -	} else {
> +	if (!test_opt(sbi, DISABLE_CHECKPOINT) &&
> +			test_opt(sbi, MERGE_CHECKPOINT)) {
>   		err = f2fs_start_ckpt_thread(sbi);
>   		if (err) {
>   			f2fs_err(sbi,
> @@ -2076,6 +2075,8 @@ static int f2fs_remount(struct super_block *sb, int *flags, char *data)
>   			    err);
>   			goto restore_gc;
>   		}
> +	} else {
> +		f2fs_stop_ckpt_thread(sbi);
>   	}
>   
>   	/*
> @@ -3831,7 +3832,8 @@ static int f2fs_fill_super(struct super_block *sb, void *data, int silent)
>   
>   	/* setup checkpoint request control and start checkpoint issue thread */
>   	f2fs_init_ckpt_req_control(sbi);
> -	if (test_opt(sbi, MERGE_CHECKPOINT)) {
> +	if (!test_opt(sbi, DISABLE_CHECKPOINT) &&
> +			test_opt(sbi, MERGE_CHECKPOINT)) {
>   		err = f2fs_start_ckpt_thread(sbi);
>   		if (err) {
>   			f2fs_err(sbi,
>