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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: Jack Steiner <steiner@sgi.com>
Subject: Re: [patch 12/13] GRU Driver V3 -  export is_uv_system(), zap_page_range() & follow_page()
Date: Tue, 8 Jul 2008 12:16:21 +1000
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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
References: <20080703213348.489120321@attica.americas.sgi.com> <Pine.LNX.4.64.0807071657450.17825@blonde.site> <20080707165358.GA16420@sgi.com>
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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.
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