Date: Wed, 9 Jul 2008 14:11:46 -0500
From: Jack Steiner <steiner@sgi.com>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Hugh Dickins <hugh@veritas.com>, Christoph Hellwig <hch@infradead.org>,
       cl@linux-foundation.org, akpm@osdl.org, linux-kernel@vger.kernel.org,
       mingo@elte.hu, tglx@linutronix.de, holt@sgi.com, andrea@qumranet.com,
       linux-mm@kvack.org
Subject: Re: [patch 12/13] GRU Driver V3 -  export is_uv_system(), zap_page_range() & follow_page()
Message-ID: <20080709191146.GA6251@sgi.com>
References: <20080703213348.489120321@attica.americas.sgi.com> <Pine.LNX.4.64.0807071657450.17825@blonde.site> <20080707165358.GA16420@sgi.com> <200807081216.22029.nickpiggin@yahoo.com.au>
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On Tue, Jul 08, 2008 at 12:16:21PM +1000, Nick Piggin wrote:
> On Tuesday 08 July 2008 02:53, Jack Steiner wrote:
> > On Mon, Jul 07, 2008 at 05:29:54PM +0100, Hugh Dickins wrote:
> 
> > > Maybe study the assumptions Nick is making in his arch/x86/mm/gup.c
> > > in mm, and do something similar in your GRU driver (falling back to
> > > the slow method when anything's not quite right).  It's not nice to
> > > have such code out in a driver, but GRU is going to be exceptional,
> > > and it may be better to have it out there than pretence of generality
> > > in the core mm exporting it.
> >
> > Ok, I'll take this approach. Open code a pagetable walker into the GRU
> > driver using the ideas of fast_gup(). This has the added benefit of being
> > able to optimize for exactly what is needed for the GRU. For example,
> > nr_pages is always 1 (at least in the current design).
> 
> Well... err, it's pretty tied to the arch and mm design. I'd rather
> if you could just make another entry point to gup.c (perhaps, one
> which doesn't automatically fall back to the get_user_pages slowpath
> for you) rather than code it again in your driver.

Long term, that is probably a good idea. However, for the short term & while
the GRU is stabilizing, I would prefer to keep the code in the driver itself.
I can address the issue of moving it to gup.c later.

I'll post the new GRU patch in a few minutes.

--- jack
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