Re: [PATCH 6/9] sunrpc/cache: retry cache lookups that return -ETIMEDOUT

[Neil Brown <neilb@suse.de>]

On Fri, 4 Dec 2009 20:17:42 -0500
"J. Bruce Fields" <bfields@fieldses.org> wrote:

> > 
> > How about this as an alternate.  I have only compile tested it, nothing more.
> > But if it looks good to you I'll make sure it really works.  
> 
> Well, without having really thinking about it:
> 
> 	- If this were two separate patches, I'd have an easier time
> 	  sorting out the interesting stuff from the trivial (though
> 	  nevertheless good) hash-function reshuffling.

I'll see what I can come up with...

> 	- Adding code to the common lookup_and_check() instead of to
> 	  every caller certainly seems better, but too bad about the
> 	  special cases that remain.

yeah.... I could possibly add a pass-by-reference to lookup_and_check
which points to a possible cached value, but that would have
only one user, so the special case would be moved elsewhere...
??

> 	- Something still seems odd here: we shouldn't ever have
> 	  duplicate cache entries with the same key, because during
> 	  their lifetimes cache entries are always kept in the hash.  So
> 	  why do we need extra code to check for that case?  I may just
> 	  be forgetting what we're doing here.  Should I go reread the
> 	  rest of the series?

When sunrpc_update_cache is called to update and item that is
already valid, it unhashes that item and creates a new one.
(The unhashed item disappears once all the refcounts go).
So if we wait for user-space to update an entry for us, we
might find out that it has been unhashed, so we need to find
the new one.

NeilBrown