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From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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Date: Tue, 08 Feb 2005 08:35:01 +1100
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Cc: linuxppc64-dev <linuxppc64-dev@ozlabs.org>,
	Arjan van de Ven <arjan@infradead.org>,
	Linux Kernel list <linux-kernel@vger.kernel.org>,
	linuxppc-dev list <linuxppc-dev@ozlabs.org>
Subject: Re: question on symbol exports
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On Mon, 2005-02-07 at 08:44 -0600, Chris Friesen wrote:
> Benjamin Herrenschmidt wrote:
> >>It turns out that to call ptep_clear_flush_dirty() on ppc64 from a 
> >>module I needed to export the following symbols:
> >>
> >>__flush_tlb_pending
> >>ppc64_tlb_batch
> >>hpte_update
> > 
> > 
> > Any reason why you need to call that from a module ? Is the module
> > GPL'd ?
> 
> I explained this at the beginning of the thread, but I'll do so again. 
> The module will be released under the GPL.
> 
> The basic idea is that we want to be able to track pages dirtied by a 
> userspace process.  The system has no swap, so we use the dirty bit for 
> this.  On demand we look up the page tables for an address range 
> specified by the caller, store the addresses of any dirty pages, then 
> mark them clean so that the next write causes them to get marked dirty 
> again.  It is this act of marking them clean that requires the 
> additional exports.
> 
> I've included the current code below.  If there is any way to accomplish 
> this without the additional exports, I'd love to hear about it.

Interesting... more than no swap, you must also make sure you have no
r/w mmap'ed file (which are technically equivalent to swap).

I'm not too fan about exporting those symbols, but I'll talk to paulus,
it should be possible at least to EXPORT_SYMBOL_GPL them...

Ben.