On 2012-05-14, at 8:06, "J. Bruce Fields" <bfields@xxxxxxxxxxxx> wrote:
> knfsd needs i_version updates on, as will userspace nfs servers and
> probably others.
>
> The only effects are that inode->i_version is bumped (under the i_lock)
> in more places, and that ->dirty_inode(I_DIRTY_DATASYNC) may be called
> more frequently than once per jiffy on write (see file_update_time).
> However the latter appears to be mostly a no-op in that case.
I thought this can have noticeable performance impact, since ext4_mark_inode_dirty() is quite heavyweight?
This is one of the reasons that the i_version update is conditional. If someone is exporting a filesystem from userspace the should be able to turn this on as a mount option, and knfsd could do it from inside the kernel. Why add overhead when it is not needed?
> So, simplify our life and just keep this feature turned on all the time.
>
> Signed-off-by: J. Bruce Fields <bfields@xxxxxxxxxx>
> ---
> fs/ext4/super.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> If people are worried that the performance impact isn't obvious, I'll
> find the time somehow to test this properly....
>
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index e1fb1d5..a99f827 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1483,7 +1483,7 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
> sbi->s_mount_flags |= EXT4_MF_FS_ABORTED;
> return 1;
> case Opt_i_version:
> - sb->s_flags |= MS_I_VERSION;
> + /* no-op; this is on by default now */
> return 1;
> case Opt_journal_dev:
> if (is_remount) {
> @@ -2979,6 +2979,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
> goto out_free_orig;
> }
> sb->s_fs_info = sbi;
> + sb->s_flags |= MS_I_VERSION;
> sbi->s_mount_opt = 0;
> sbi->s_resuid = EXT4_DEF_RESUID;
> sbi->s_resgid = EXT4_DEF_RESGID;
> --
> 1.7.9.5
>
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