linux-kernel - Re: [PATCH v3 16/19] fs: only set S_VERSION when updating times if necessary

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Message-ID: <20171218160736.GE30350@quack2.suse.cz>
Date:   Mon, 18 Dec 2017 17:07:36 +0100
From:   Jan Kara <jack@...e.cz>
To:     Jeff Layton <jlayton@...nel.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        viro@...iv.linux.org.uk, linux-nfs@...r.kernel.org,
        bfields@...ldses.org, neilb@...e.de, jack@...e.de,
        linux-ext4@...r.kernel.org, tytso@....edu,
        adilger.kernel@...ger.ca, linux-xfs@...r.kernel.org,
        darrick.wong@...cle.com, david@...morbit.com,
        linux-btrfs@...r.kernel.org, clm@...com, jbacik@...com,
        dsterba@...e.com, linux-integrity@...r.kernel.org,
        zohar@...ux.vnet.ibm.com, dmitry.kasatkin@...il.com,
        linux-afs@...ts.infradead.org, dhowells@...hat.com,
        jaltman@...istor.com
Subject: Re: [PATCH v3 16/19] fs: only set S_VERSION when updating times if
 necessary

On Mon 18-12-17 10:11:53, 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 | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/inode.c b/fs/inode.c
> index 03102d6ef044..83f6cfc3cde7 100644
> --- a/fs/inode.c
> +++ b/fs/inode.c
> @@ -19,6 +19,7 @@
>  #include <linux/ratelimit.h>
>  #include <linux/list_lru.h>
>  #include <trace/events/writeback.h>
> +#include <linux/iversion.h>
>  #include "internal.h"
>  
>  /*
> @@ -1634,17 +1635,24 @@ 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 = false;
>  
> -	if (flags & S_ATIME)
> +	if (flags & S_ATIME) {
>  		inode->i_atime = *time;
> +		dirty |= !(inode->i_sb->s_flags & SB_LAZYTIME);
> +	}
>  	if (flags & S_VERSION)
> -		inode_inc_iversion(inode);
> -	if (flags & S_CTIME)
> +		dirty |= inode_maybe_inc_iversion(inode, dirty);
> +	if (flags & S_CTIME) {
>  		inode->i_ctime = *time;
> -	if (flags & S_MTIME)
> +		dirty = true;
> +	}
> +	if (flags & S_MTIME) {
>  		inode->i_mtime = *time;
> +		dirty = true;
> +	}

The SB_LAZYTIME handling is wrong here. That option is not only about atime
handling but rather about all inode time stamps. So you rather need
something like:

	if (flags & (S_ATIME | S_CTIME | S_MTIME) &&
	    !(inode->i_sb->s_flags & SB_LAZYTIME))
		dirty = true;

								Honza

>  
> -	if (!(inode->i_sb->s_flags & SB_LAZYTIME) || (flags & S_VERSION))
> +	if (dirty)
>  		iflags |= I_DIRTY_SYNC;
>  	__mark_inode_dirty(inode, iflags);
>  	return 0;
> @@ -1863,7 +1871,7 @@ 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)
> -- 
> 2.14.3
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR