Re: atimes not updated over NFS

[Frank van Maarseveen <frankvm@frankvm.com>]

On Mon, Jan 21, 2008 at 02:31:05PM -0500, Trond Myklebust wrote:
> 
> On Mon, 2008-01-21 at 14:06 -0500, J. Bruce Fields wrote:
> > > > > Commands to reproduce this problem on the client:
> > > > > 
> > > > > 	dd </dev/zero >testfile count=1
> > > > > 	ls -l --time=atime --full-time testfile
> > > > > 	sleep 2
> > > > > 	wc testfile
> > > > > 	ls -l --time=atime --full-time testfile
> > > > > 		(same atime, not good)
> > > > 
> > > > Can you confirm that it does not change on the server? If so, then we
> > > > need to look at the server for a fix. The client should only be
> > > > mirroring the server's idea of the correct atime.
> > > 
> > > It doesn't change on the server (2.6.23.12)
> > 
> > That still leaves open the question as to whether this is due to changes
> > in the client that are causing it not to issue a read to the server when
> > it would have before, or whether the server is just refusing to update
> > the atime on read for some reason....
> 
> A script of the form

"rm -f testfile" and at least one "touch ." in advance to get deterministic behavior.

> 
>                 ssh server 'dd </dev/zero >testfile count=1; ls -l --time=atime --full-time testfile'

put a sleep 2 here.

>                 
>                 cat testfile >/dev/null

put a sleep 2 here just in case we would race with something in flight

>                 
>                 ssh server 'ls -l --time=atime --full-time testfile'
>                 ls -l --time=atime --full-time testfile
> 

I tried some kernels (same on client and server). There are three atimes
after each experiment.

2.6.21.7:
	t
	t + 2
	t + 2

This seems to work but it doesn't: only the first "cat testfile" will
update the atime. Subsequent cat commands will not update atime unless
"cat" is executed on the server.

2.6.22.10:
	t
	t + 2
	t + 2

(same behavior)

2.6.23.12:
	t
	t
	t

definately not good. "cat" on the server updates atime again.


Trying a different combination of kernels:

server 2.6.23.12, client 2.6.22.10:
	t
	t
	t

server 2.6.22.10, client 2.6.23.12:
	t
	t + 2
	t + 2

so, there are 2 phenomena and one has been introduced with 2.6.23 on
the server side. Filesystem on the server is ext3.

-- 
Frank