From: Dan Williams <dan.j.williams@intel.com>
To: "Jérôme Glisse" <jglisse@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>, Linux MM <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
"Rafael J. Wysocki" <rafael@kernel.org>,
Ross Zwisler <ross.zwisler@linux.intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Haggai Eran <haggaie@mellanox.com>,
balbirs@au1.ibm.com,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
"Kuehling, Felix" <felix.kuehling@amd.com>,
Philip.Yang@amd.com, "Koenig,
Christian" <christian.koenig@amd.com>,
"Blinzer, Paul" <Paul.Blinzer@amd.com>,
Logan Gunthorpe <logang@deltatee.com>,
John Hubbard <jhubbard@nvidia.com>,
rcampbell@nvidia.com
Subject: Re: [RFC PATCH 02/14] mm/hms: heterogenenous memory system (HMS) documentation
Date: Tue, 4 Dec 2018 11:19:23 -0800 [thread overview]
Message-ID: <CAPcyv4iddjvOvdRRRMrD5RtrVzLB13cPATbpE52ZcuPWWsyx-w@mail.gmail.com> (raw)
In-Reply-To: <20181204185725.GE2937@redhat.com>
On Tue, Dec 4, 2018 at 10:58 AM Jerome Glisse <jglisse@redhat.com> wrote:
>
> On Tue, Dec 04, 2018 at 10:31:17AM -0800, Dan Williams wrote:
> > On Tue, Dec 4, 2018 at 10:24 AM Jerome Glisse <jglisse@redhat.com> wrote:
> > >
> > > On Tue, Dec 04, 2018 at 09:06:59AM -0800, Andi Kleen wrote:
> > > > jglisse@redhat.com writes:
> > > >
> > > > > +
> > > > > +To help with forward compatibility each object as a version value and
> > > > > +it is mandatory for user space to only use target or initiator with
> > > > > +version supported by the user space. For instance if user space only
> > > > > +knows about what version 1 means and sees a target with version 2 then
> > > > > +the user space must ignore that target as if it does not exist.
> > > >
> > > > So once v2 is introduced all applications that only support v1 break.
> > > >
> > > > That seems very un-Linux and will break Linus' "do not break existing
> > > > applications" rule.
> > > >
> > > > The standard approach that if you add something incompatible is to
> > > > add new field, but keep the old ones.
> > >
> > > No that's not how it is suppose to work. So let says it is 2018 and you
> > > have v1 memory (like your regular main DDR memory for instance) then it
> > > will always be expose a v1 memory.
> > >
> > > Fast forward 2020 and you have this new type of memory that is not cache
> > > coherent and you want to expose this to userspace through HMS. What you
> > > do is a kernel patch that introduce the v2 type for target and define a
> > > set of new sysfs file to describe what v2 is. On this new computer you
> > > report your usual main memory as v1 and your new memory as v2.
> > >
> > > So the application that only knew about v1 will keep using any v1 memory
> > > on your new platform but it will not use any of the new memory v2 which
> > > is what you want to happen. You do not have to break existing application
> > > while allowing to add new type of memory.
> >
> > That sounds needlessly restrictive. Let the kernel arbitrate what
> > memory an application gets, don't design a system where applications
> > are hard coded to a memory type. Applications can hint, or optionally
> > specify an override and the kernel can react accordingly.
>
> You do not want to randomly use non cache coherent memory inside your
> application :)
The kernel arbitrates memory, it's a bug if it hands out something
that exotic to an unaware application.
next prev parent reply other threads:[~2018-12-04 19:19 UTC|newest]
Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-03 23:34 [RFC PATCH 00/14] Heterogeneous Memory System (HMS) and hbind() jglisse
2018-12-03 23:34 ` [RFC PATCH 01/14] mm/hms: heterogeneous memory system (sysfs infrastructure) jglisse
2018-12-03 23:34 ` [RFC PATCH 02/14] mm/hms: heterogenenous memory system (HMS) documentation jglisse
2018-12-04 17:06 ` Andi Kleen
2018-12-04 18:24 ` Jerome Glisse
2018-12-04 18:31 ` Dan Williams
2018-12-04 18:57 ` Jerome Glisse
2018-12-04 19:11 ` Logan Gunthorpe
2018-12-04 19:22 ` Jerome Glisse
2018-12-04 19:41 ` Logan Gunthorpe
2018-12-04 20:13 ` Jerome Glisse
2018-12-04 20:30 ` Logan Gunthorpe
2018-12-04 20:59 ` Jerome Glisse
2018-12-04 21:19 ` Logan Gunthorpe
2018-12-04 21:51 ` Jerome Glisse
2018-12-04 22:16 ` Logan Gunthorpe
2018-12-04 23:56 ` Jerome Glisse
2018-12-05 1:15 ` Logan Gunthorpe
2018-12-05 2:31 ` Jerome Glisse
2018-12-05 17:41 ` Logan Gunthorpe
2018-12-05 18:07 ` Jerome Glisse
2018-12-05 18:20 ` Logan Gunthorpe
2018-12-05 18:33 ` Jerome Glisse
2018-12-05 18:48 ` Logan Gunthorpe
2018-12-05 18:55 ` Jerome Glisse
2018-12-05 19:10 ` Logan Gunthorpe
2018-12-05 22:58 ` Jerome Glisse
2018-12-05 23:09 ` Logan Gunthorpe
2018-12-05 23:20 ` Jerome Glisse
2018-12-05 23:23 ` Logan Gunthorpe
2018-12-05 23:27 ` Jerome Glisse
2018-12-06 0:08 ` Dan Williams
2018-12-05 2:34 ` Dan Williams
2018-12-05 2:37 ` Jerome Glisse
2018-12-05 17:25 ` Logan Gunthorpe
2018-12-05 18:01 ` Jerome Glisse
2018-12-04 20:14 ` Andi Kleen
2018-12-04 20:47 ` Logan Gunthorpe
2018-12-04 21:15 ` Jerome Glisse
2018-12-04 19:19 ` Dan Williams [this message]
2018-12-04 19:32 ` Jerome Glisse
2018-12-04 20:12 ` Andi Kleen
2018-12-04 20:41 ` Jerome Glisse
2018-12-05 4:36 ` Aneesh Kumar K.V
2018-12-05 4:41 ` Jerome Glisse
2018-12-05 10:52 ` Mike Rapoport
2018-12-03 23:34 ` [RFC PATCH 03/14] mm/hms: add target memory to heterogeneous memory system infrastructure jglisse
2018-12-03 23:34 ` [RFC PATCH 04/14] mm/hms: add initiator " jglisse
2018-12-03 23:35 ` [RFC PATCH 05/14] mm/hms: add link " jglisse
2018-12-03 23:35 ` [RFC PATCH 06/14] mm/hms: add bridge " jglisse
2018-12-03 23:35 ` [RFC PATCH 07/14] mm/hms: register main memory with heterogenenous memory system jglisse
2018-12-03 23:35 ` [RFC PATCH 08/14] mm/hms: register main CPUs " jglisse
2018-12-03 23:35 ` [RFC PATCH 09/14] mm/hms: hbind() for heterogeneous memory system (aka mbind() for HMS) jglisse
2018-12-03 23:35 ` [RFC PATCH 10/14] mm/hbind: add heterogeneous memory policy tracking infrastructure jglisse
2018-12-03 23:35 ` [RFC PATCH 11/14] mm/hbind: add bind command to heterogeneous memory policy jglisse
2018-12-03 23:35 ` [RFC PATCH 12/14] mm/hbind: add migrate command to hbind() ioctl jglisse
2018-12-03 23:35 ` [RFC PATCH 13/14] drm/nouveau: register GPU under heterogeneous memory system jglisse
2018-12-03 23:35 ` [RFC PATCH 14/14] test/hms: tests for " jglisse
2018-12-04 7:44 ` [RFC PATCH 00/14] Heterogeneous Memory System (HMS) and hbind() Aneesh Kumar K.V
2018-12-04 14:44 ` Jerome Glisse
2018-12-04 18:02 ` Dave Hansen
2018-12-04 18:49 ` Jerome Glisse
2018-12-04 18:54 ` Dave Hansen
2018-12-04 19:11 ` Jerome Glisse
2018-12-04 21:37 ` Dave Hansen
2018-12-04 21:57 ` Jerome Glisse
2018-12-04 23:58 ` Dave Hansen
2018-12-05 0:29 ` Jerome Glisse
2018-12-05 1:22 ` Kuehling, Felix
2018-12-05 11:27 ` Aneesh Kumar K.V
2018-12-05 16:09 ` Jerome Glisse
2018-12-04 23:54 ` Dave Hansen
2018-12-05 0:15 ` Jerome Glisse
2018-12-05 1:06 ` Dave Hansen
2018-12-05 2:13 ` Jerome Glisse
2018-12-05 17:27 ` Dave Hansen
2018-12-05 17:53 ` Jerome Glisse
2018-12-06 18:25 ` Dave Hansen
2018-12-06 19:20 ` Jerome Glisse
2018-12-06 19:31 ` Dave Hansen
2018-12-06 20:11 ` Logan Gunthorpe
2018-12-06 22:04 ` Dave Hansen
2018-12-06 22:39 ` Jerome Glisse
2018-12-06 23:09 ` Dave Hansen
2018-12-06 23:28 ` Logan Gunthorpe
2018-12-06 23:34 ` Dave Hansen
2018-12-06 23:38 ` Dave Hansen
2018-12-06 23:48 ` Logan Gunthorpe
2018-12-07 0:20 ` Jerome Glisse
2018-12-07 15:06 ` Jonathan Cameron
2018-12-07 19:37 ` Jerome Glisse
2018-12-07 0:15 ` Jerome Glisse
2018-12-06 20:27 ` Jerome Glisse
2018-12-06 21:46 ` Jerome Glisse
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