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

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Date:   Mon, 18 Dec 2017 12:25:38 -0500
From:   Jeff Layton <jlayton@...nel.org>
To:     Jan Kara <jack@...e.cz>
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, 2017-12-18 at 17:07 +0100, Jan Kara wrote:
> 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
> 

Thanks. I misunderstood that. Will fix.

> >  
> > -	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
> > 

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