linux-kernel - Re: [RFC PATCH] ceph: initialize superblock s_time

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Date:   Thu, 27 Jun 2019 15:44:31 +0000 (UTC)
From:   Sage Weil <sweil@...hat.com>
To:     Jeff Layton <jlayton@...nel.org>
cc:     Luis Henriques <lhenriques@...e.com>,
        "Yan, Zheng" <zyan@...hat.com>, Ilya Dryomov <idryomov@...il.com>,
        ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] ceph: initialize superblock s_time_gran to 1

On Thu, 27 Jun 2019, Jeff Layton wrote:
> On Thu, 2019-06-27 at 14:51 +0100, Luis Henriques wrote:
> > Having granularity set to 1us results in having inode timestamps with a
> > accurancy different from the fuse client (i.e. atime, ctime and mtime will
> > always end with '000').  This patch normalizes this behaviour and sets the
> > granularity to 1.
> > 
> > Signed-off-by: Luis Henriques <lhenriques@...e.com>
> > ---
> >  fs/ceph/super.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > Hi!
> > 
> > As far as I could see there are no other side-effects of changing
> > s_time_gran but I'm really not sure why it was initially set to 1000 in
> > the first place so I may be missing something.
> > 
> > diff --git a/fs/ceph/super.c b/fs/ceph/super.c
> > index d57fa60dcd43..35dd75bc9cd0 100644
> > --- a/fs/ceph/super.c
> > +++ b/fs/ceph/super.c
> > @@ -980,7 +980,7 @@ static int ceph_set_super(struct super_block *s, void *data)
> >  	s->s_d_op = &ceph_dentry_ops;
> >  	s->s_export_op = &ceph_export_ops;
> >  
> > -	s->s_time_gran = 1000;  /* 1000 ns == 1 us */
> > +	s->s_time_gran = 1;
> >  
> >  	ret = set_anon_super(s, NULL);  /* what is that second arg for? */
> >  	if (ret != 0)
> 
> 
> Looks like it was set that way since the client code was originally
> merged. Was this an earlier limitation of ceph that is no longer
> applicable?
> 
> In any case, I see no need at all to keep this at 1000, so:

As long as the encoded on-write time value is at ns resolution, I 
agree!  No recollection of why I did this :(

Reviewed-by: Sage Weil <sage@...hat.com>