linux-kernel - Re: [PATCH 16/19] fs: only set S_VERSION when updating times if necessary

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Date:   Fri, 15 Dec 2017 07:59:51 -0500
From:   Jeff Layton <jlayton@...nel.org>
To:     linux-fsdevel@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, hch@....de, neilb@...e.de,
        bfields@...ldses.org, amir73il@...il.com, jack@...e.de,
        viro@...iv.linux.org.uk, David Howells <dhowells@...hat.com>
Subject: Re: [PATCH 16/19] fs: only set S_VERSION when updating times if
 necessary

On Wed, 2017-12-13 at 09:20 -0500, Jeff Layton wrote:
> From: Jeff Layton <jlayton@...hat.com>
> 
> We only really need to update i_version if someone has queried for it
> since we last incremented it. By doing that, we can avoid having to
> update the inode if the times haven't changed.
> 
> If the times have changed, then we go ahead and forcibly increment the
> counter, under the assumption that we'll be going to the storage
> anyway, and the increment itself is relatively cheap.
> 
> Signed-off-by: Jeff Layton <jlayton@...hat.com>
> ---
>  fs/inode.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 03102d6ef044..7f4215f4309c 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -1634,17 +1634,18 @@ static int relatime_need_update(const struct path *path, struct inode *inode,
>  int generic_update_time(struct inode *inode, struct timespec *time, int flags)
>  {
>  	int iflags = I_DIRTY_TIME;
> +	bool dirty = flags & ~S_VERSION;
>  
>  	if (flags & S_ATIME)
>  		inode->i_atime = *time;
> -	if (flags & S_VERSION)
> -		inode_inc_iversion(inode);
>  	if (flags & S_CTIME)
>  		inode->i_ctime = *time;
>  	if (flags & S_MTIME)
>  		inode->i_mtime = *time;
> +	if (flags & S_VERSION)
> +		dirty |= inode_maybe_inc_iversion(inode, dirty);
>  
> -	if (!(inode->i_sb->s_flags & SB_LAZYTIME) || (flags & S_VERSION))
> +	if (dirty || !(inode->i_sb->s_flags & SB_LAZYTIME))

David Howells pointed out that the logic for setting dirty in here will
break SB_LAZYTIME handling. The patch is now fixed in my tree.

>  		iflags |= I_DIRTY_SYNC;
>  	__mark_inode_dirty(inode, iflags);
>  	return 0;
> @@ -1863,7 +1864,7 @@ int file_update_time(struct file *file)
>  	if (!timespec_equal(&inode->i_ctime, &now))
>  		sync_it |= S_CTIME;
>  
> -	if (IS_I_VERSION(inode))
> +	if (IS_I_VERSION(inode) && inode_iversion_need_inc(inode))
>  		sync_it |= S_VERSION;
>  
>  	if (!sync_it)

-- 
Jeff Layton <jlayton@...nel.org>