linux-ext4 - Re: barriers off by default?

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Date:	Sat, 17 May 2008 14:02:57 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Theodore Tso <tytso@....edu>
CC:	Jan Kara <jack@...e.cz>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: barriers off by default?

Theodore Tso wrote:
> Given the discussion on the other thread about the performance impact
> and hard-to-hit nature of barrier problems, how about this?

I still want to do a bit of testing to see if it's really that hard to
hit :)  (trying to hook up my x10-power-killer is a challenge with no
serial ports....)

But in any case, adding these to potential default mount options sounds
good to me.

-Eric

>     		       	  	  	    	- Ted
> 
> ext4: Add EXT4_DEFM_BARRIER and EXT4_DEFM_I_VERSION default mount options
> 
> Allow the i_version and barrier mount options to be set by default via
> flags in the ext4 superblock.
> 
> Signed-off-by: "Theodore Ts'o" <tytso@....edu>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index b7ffb91..afeba1f 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -785,6 +785,8 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
>  #define EXT4_DEFM_JMODE_DATA	0x0020
>  #define EXT4_DEFM_JMODE_ORDERED	0x0040
>  #define EXT4_DEFM_JMODE_WBACK	0x0060
> +#define EXT4_DEFM_BARRIER	0x0080
> +#define EXT4_DEFM_I_VERSION	0x0100
>  
>  /*
>   * Structure of a directory entry
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 09d9359..c0a657c 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -729,7 +729,7 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
>  		seq_printf(seq, ",commit=%u",
>  			   (unsigned) (sbi->s_commit_interval / HZ));
>  	}
> -	if (test_opt(sb, BARRIER))
> +	if (test_opt(sb, BARRIER) && !(def_mount_opts & EXT4_DEFM_BARRIER))
>  		seq_puts(seq, ",barrier=1");
>  	if (test_opt(sb, NOBH))
>  		seq_puts(seq, ",nobh");
> @@ -737,7 +737,7 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
>  		seq_puts(seq, ",noextents");
>  	if (!test_opt(sb, MBALLOC))
>  		seq_puts(seq, ",nomballoc");
> -	if (test_opt(sb, I_VERSION))
> +	if (test_opt(sb, I_VERSION) && !(def_mount_opts & EXT4_DEFM_I_VERSION))
>  		seq_puts(seq, ",i_version");
>  
>  	if (sbi->s_stripe)
> @@ -1896,6 +1896,12 @@ static int ext4_fill_super (struct super_block *sb, void *data, int silent)
>  	else if ((def_mount_opts & EXT4_DEFM_JMODE) == EXT4_DEFM_JMODE_WBACK)
>  		sbi->s_mount_opt |= EXT4_MOUNT_WRITEBACK_DATA;
>  
> +	if (def_mount_opts & EXT4_DEFM_BARRIER)
> +		set_opt(sbi->s_mount_opt, BARRIER);
> +
> +	if (def_mount_opts & EXT4_DEFM_I_VERSION)
> +		sb->s_flags |= MS_I_VERSION;
> +
>  	if (le16_to_cpu(sbi->s_es->s_errors) == EXT4_ERRORS_PANIC)
>  		set_opt(sbi->s_mount_opt, ERRORS_PANIC);
>  	else if (le16_to_cpu(sbi->s_es->s_errors) == EXT4_ERRORS_CONTINUE)

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