Subject: RE: [NFSv4] Hints for client on LAYOUTRECALL

From: [email-masked]
Date: Tue, 15 Aug 2006 11:35:36 -0400

On Fri, 11 Aug 2006 11:54:01 -0400, Trond Myklebust wrote: 
> On Fri, 2006-08-11 at 11:39 -0400, fridella_stephen at emc.com wrote:
> > Now that I understand the caching part (finally!) I still think there
> > is value in a hint for LAYOUTRECALL.  While the RECALL does not cause
> > the client to flush data, it will cause the client to commit changes in
the
> > layout for any blocks which have already been written.  These changes
> > must be processed by the server, recorded in the fs transaction log,
etc.
> > In the truncate case, all such changes will be wiped out once the
truncate
> > occurs, meaning that the work to commit them was wasted effort.  If a
> > LAYOUTRECALL contains a hint indicating it is the result of a truncate,
> > the client can simply return the LAYOUT without committing changes.
> 
> I s'pose so.
> 
> > Since we have already allocated a field for one type of LAYOUTRECALL
> > hint ("layoutchanged"), why not use the field more generically to
> > carry multiple kinds of useful hints?
> 
> Examples?
> 
> Cheers,
>   Trond

Well I really only have the two examples so far:

layoutchanged (used by file layout)
layouttruncate (used by block/vol layout)

One reason for starting this thread was to see if the object-layout
or file-layout guys had other "hints" that they would like to send on
LAYOUTRECALL.  Garth, Benny --- what about it?  Any interest?

-Steve

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---

From: Benny Halevy <[email-masked]>
Date: Tue, 22 Aug 2006 12:37:28 +0300

> LAYOUTRECALL.  Garth, Benny --- what about it?  Any interest?

In my opinion, adding hints to cb_layoutreturn is a a bad idea.  I'd 
prefer to
add new callback operations if you need extra semantics rather than 
piggybacking
these as hints to cb_layoutrecall.  This will allow you to clearly 
separate the
semantics, document them better, pass the arguments, results, and error 
codes
you really need, etc.  Passing hints also opens a door to non-standard 
implementations.

That said, I see no immediate need for a hint to cb_layoutrecall for 
object layouts :)

Benny