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Date: Mon, 7 Jul 2008 14:29:23 -0500 From: Jack Steiner <steiner@....com> To: Arjan van de Ven <arjan@...radead.org> Cc: Hugh Dickins <hugh@...itas.com>, Christoph Hellwig <hch@...radead.org>, Nick Piggin <nickpiggin@...oo.com.au>, cl@...ux-foundation.org, akpm@...l.org, linux-kernel@...r.kernel.org, mingo@...e.hu, tglx@...utronix.de, holt@....com, andrea@...ranet.com, linux-mm@...ck.org Subject: Re: [patch 12/13] GRU Driver V3 - export is_uv_system(), zap_page_range() & follow_page() On Mon, Jul 07, 2008 at 11:58:44AM -0700, Arjan van de Ven wrote: > On Mon, 7 Jul 2008 17:29:54 +0100 (BST) > Hugh Dickins <hugh@...itas.com> wrote: > > > On Mon, 7 Jul 2008, Jack Steiner wrote: > > > > > +EXPORT_SYMBOL_GPL(follow_page); > > > > > > > > NACK. > > > > > > > > These should never be called by a driver and suggest you need to > > > > rething your VM integration in this driver. > > > > > > Can you provide some additional details on the type of kernel API > > > that could be exported to provide a pte lookup in atomic context? > > > > I don't see EXPORT_SYMBOL_GPL(follow_page) as objectionable myself: > > it rather seems rather to complement EXPORT_SYMBOL(vm_insert_page) > > and EXPORT_SYMBOL(vmalloc_to_page); though I'd agree that it's > > sufficiently sensitive to need that _GPL on it. > > > > ... > > > > > Currently, the driver calls follow_page() in interrupt context. > > > > However, that's a problem, isn't it, given the pte_offset_map_lock > > in follow_page? To avoid the possibility of deadlock, wouldn't we > > have to change all the page table locking to irq-disabling variants? > > Which I think we'd have reason to prefer not to do. > > > > 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. > > > > I wonder if GRU even should be a module; it sounds rather like pretty > core functionality and if it's this invasive to the VM it probably > should be a real part of the VM instead The GRU is not actually very invasive into the VM. It will use the new MMU-notifier callbacks. Aside from the need to translate virt->physical & zap ptes belonging to the GRU, it works fine as a module. No other core changes are needed. An additional advantage in keeping it as a module is that I expect it to under a number of changes as the hardware matures. It is easier to update the GRU if it is a module. --- jack -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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