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Date:   Wed, 27 Jul 2022 11:48:39 -0400
From:   "Benjamin Coddington" <bcodding@...hat.com>
To:     "Jeff Layton" <jlayton@...nel.org>
Cc:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, "Dave Chinner" <david@...morbit.com>,
        "Lukas Czerner" <lczerner@...hat.com>,
        "Christoph Hellwig" <hch@...radead.org>,
        "Darrick J . Wong" <djwong@...nel.org>
Subject: Re: [PATCH v2] ext4: unconditionally enable the i_version counter

On 27 Jul 2022, at 10:37, Jeff Layton wrote:

> The original i_version implementation was pretty expensive, requiring 
> a
> log flush on every change. Because of this, it was gated behind a 
> mount
> option (implemented via the MS_I_VERSION mountoption flag).
>
> Commit ae5e165d855d (fs: new API for handling inode->i_version) made 
> the
> i_version flag much less expensive, so there is no longer a 
> performance
> penalty from enabling it. xfs and btrfs already enable it
> unconditionally when the on-disk format can support it.
>
> Have ext4 ignore the SB_I_VERSION flag, and just enable it
> unconditionally. While we're in here, remove the handling of
> Opt_i_version as well, since we're almost to 5.20 anyway.
>
> Ideally, we'd couple this change with a way to disable the i_version
> counter (just in case), but the way the iversion mount option was
> implemented makes that difficult to do. We'd need to add a new mount
> option altogether or do something with tune2fs. That's probably best
> left to later patches if it turns out to be needed.
>
> Cc: Dave Chinner <david@...morbit.com>
> Cc: Lukas Czerner <lczerner@...hat.com>
> Cc: Benjamin Coddington <bcodding@...hat.com>
> Cc: Christoph Hellwig <hch@...radead.org>
> Cc: Darrick J. Wong <djwong@...nel.org>
> Signed-off-by: Jeff Layton <jlayton@...nel.org>
> ---
>  fs/ext4/inode.c |  5 ++---
>  fs/ext4/super.c | 13 ++++---------
>  2 files changed, 6 insertions(+), 12 deletions(-)
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 84c0eb55071d..c785c0b72116 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -5411,7 +5411,7 @@ int ext4_setattr(struct user_namespace 
> *mnt_userns, struct dentry *dentry,
>  			return -EINVAL;
>  		}
>
> -		if (IS_I_VERSION(inode) && attr->ia_size != inode->i_size)
> +		if (attr->ia_size != inode->i_size)
>  			inode_inc_iversion(inode);
>
>  		if (shrink) {
> @@ -5717,8 +5717,7 @@ int ext4_mark_iloc_dirty(handle_t *handle,
>  	}
>  	ext4_fc_track_inode(handle, inode);
>
> -	if (IS_I_VERSION(inode))
> -		inode_inc_iversion(inode);
> +	inode_inc_iversion(inode);
>
>  	/* the do_update_inode consumes one bh->b_count */
>  	get_bh(iloc->bh);
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 845f2f8aee5f..4b06f394d7d1 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1585,7 +1585,7 @@ enum {
>  	Opt_inlinecrypt,
>  	Opt_usrjquota, Opt_grpjquota, Opt_quota,
>  	Opt_noquota, Opt_barrier, Opt_nobarrier, Opt_err,
> -	Opt_usrquota, Opt_grpquota, Opt_prjquota, Opt_i_version,
> +	Opt_usrquota, Opt_grpquota, Opt_prjquota,
>  	Opt_dax, Opt_dax_always, Opt_dax_inode, Opt_dax_never,
>  	Opt_stripe, Opt_delalloc, Opt_nodelalloc, Opt_warn_on_error,
>  	Opt_nowarn_on_error, Opt_mblk_io_submit, Opt_debug_want_extra_isize,
> @@ -1694,7 +1694,6 @@ static const struct fs_parameter_spec 
> ext4_param_specs[] = {
>  	fsparam_flag	("barrier",		Opt_barrier),
>  	fsparam_u32	("barrier",		Opt_barrier),
>  	fsparam_flag	("nobarrier",		Opt_nobarrier),
> -	fsparam_flag	("i_version",		Opt_i_version),

We've got to keep the parameter, I think, else we'll break existing 
setups
with the i_version mount option.

Ben

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