linux-kernel - Re: [patch 0/6] MMU Notifiers V6

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Message-Id: <20080208142315.7fe4b95e.akpm@linux-foundation.org>
Date:	Fri, 8 Feb 2008 14:23:15 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Christoph Lameter <clameter@....com>
Cc:	andrea@...ranet.com, holt@....com, avi@...ranet.com,
	izike@...ranet.com, kvm-devel@...ts.sourceforge.net,
	a.p.zijlstra@...llo.nl, steiner@....com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	daniel.blueman@...drics.com, general@...ts.openfabrics.org
Subject: Re: [patch 0/6] MMU Notifiers V6

On Fri, 08 Feb 2008 14:06:16 -0800
Christoph Lameter <clameter@....com> wrote:

> This is a patchset implementing MMU notifier callbacks based on Andrea's
> earlier work. These are needed if Linux pages are referenced from something
> else than tracked by the rmaps of the kernel (an external MMU). MMU
> notifiers allow us to get rid of the page pinning for RDMA and various
> other purposes. It gets rid of the broken use of mlock for page pinning.
> (mlock really does *not* pin pages....)
> 
> More information on the rationale and the technical details can be found in
> the first patch and the README provided by that patch in
> Documentation/mmu_notifiers.
> 
> The known immediate users are
> 
> KVM
> - Establishes a refcount to the page via get_user_pages().
> - External references are called spte.
> - Has page tables to track pages whose refcount was elevated but
>   no reverse maps.
> 
> GRU
> - Simple additional hardware TLB (possibly covering multiple instances of
>   Linux)
> - Needs TLB shootdown when the VM unmaps pages.
> - Determines page address via follow_page (from interrupt context) but can
>   fall back to get_user_pages().
> - No page reference possible since no page status is kept..
> 
> XPmem
> - Allows use of a processes memory by remote instances of Linux.
> - Provides its own reverse mappings to track remote pte.
> - Established refcounts on the exported pages.
> - Must sleep in order to wait for remote acks of ptes that are being
>   cleared.
> 

What about ib_umem_get()?
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