Date: Wed, 14 Jan 2009 13:17:48 -0500
From: Kyle McMartin <kyle@infradead.org>
To: richard kennedy <richard@rsk.demon.co.uk>
Cc: Kyle McMartin <kyle@infradead.org>, Takashi Iwai <tiwai@suse.de>,
       rusty@rustcorp.com.au, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] module: kzalloc mod->ref
Message-ID: <20090114181748.GQ25103@bombadil.infradead.org>
References: <20090114033533.GL25103@bombadil.infradead.org> <s5hmydufe3c.wl%tiwai@suse.de> <20090114155859.GO25103@bombadil.infradead.org> <496E261F.9000803@rsk.demon.co.uk>
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On Wed, Jan 14, 2009 at 05:51:27PM +0000, richard kennedy wrote:
> Aside from the code in socket does this reference count really get used
> that often? Atomic_t gets used for ref counts is lots of other places in
> the kernel, so why not turn module_ref into an atomic counter & drop the
> array entirely saving all of the memory & disk space?
> 
> I do wonder if socket could manage its module lifetimes in some other
> way, then we really could just use an atomic module ref without too much
> impact. I didn't get very far in trying to work out what exactly was
> going on in socket.c but maybe it's worth another look.
> 

I suppose it depends on how much contention there will end up being on
the atomic_t, given that right now, the module_ref structure favours
writers (since readers need to loop.) 

I'd like to hear what rusty has to say, but I'm working on a patch
to do module_ref with RCU (and to allocate it in modpost with per_cpu
variables, but that needs more testing.) I'll check what kind of
difference those end up making.

> I don't have any network test harness so it's difficult to tell what
> impact any code change is going to have. Do you have any suggestions for
> a good test of this?
> 

No, but I imagine Rick Jones' netperf would show the effect, if any.

cheers, Kyle
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