linux-kernel - Re: Interacting with coherent memory on external devices

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Message-ID: <20150422131832.GU5561@linux.vnet.ibm.com>
Date:	Wed, 22 Apr 2015 06:18:32 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...ux.com>
Cc:	Jerome Glisse <j.glisse@...il.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, jglisse@...hat.com, mgorman@...e.de,
	aarcange@...hat.com, riel@...hat.com, airlied@...hat.com,
	benh@...nel.crashing.org, aneesh.kumar@...ux.vnet.ibm.com,
	Cameron Buschardt <cabuschardt@...dia.com>,
	Mark Hairgrove <mhairgrove@...dia.com>,
	Geoffrey Gerfin <ggerfin@...dia.com>,
	John McKenna <jmckenna@...dia.com>, akpm@...ux-foundation.org
Subject: Re: Interacting with coherent memory on external devices

On Tue, Apr 21, 2015 at 07:50:02PM -0500, Christoph Lameter wrote:
> On Tue, 21 Apr 2015, Jerome Glisse wrote:

[ . . . ]

> > Paul is working on a platform that is more advance that the one HMM try
> > to address and i believe the x86 platform will not have functionality
> > such a CAPI, at least it is not part of any roadmap i know about for
> > x86.
> 
> We will be one of the first users of Paul's Platform. Please do not do
> crazy stuff but give us a sane solution where we can control the
> hardware. No strange VM hooks that automatically move stuff back and forth
> please. If you do this we will have to disable them anyways because they
> would interfere with our needs to have the code not be disturbed by random
> OS noise. We need detailed control as to when and how we move data.

I completely agree that some critically important use cases, such as
yours, will absolutely require that the application explicitly choose
memory placement and have the memory stay there.

Requirement 2 was supposed to be getting at this by saying "explicitly
or implicitly allocated", with the "explicitly" calling out your use
case.  How should I reword this to better bring this out?

							Thanx, Paul

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