From: Wei Xu <weixugc@google.com>
To: "ying.huang@intel.com" <ying.huang@intel.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
Alistair Popple <apopple@nvidia.com>,
Yang Shi <shy828301@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Dan Williams <dan.j.williams@intel.com>,
Linux MM <linux-mm@kvack.org>, Greg Thelen <gthelen@google.com>,
Jagdish Gediya <jvgediya@linux.ibm.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Michal Hocko <mhocko@kernel.org>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
Brice Goglin <brice.goglin@gmail.com>,
Feng Tang <feng.tang@intel.com>,
Jonathan Cameron <Jonathan.Cameron@huawei.com>,
Tim Chen <tim.c.chen@linux.intel.com>
Subject: Re: RFC: Memory Tiering Kernel Interfaces
Date: Wed, 11 May 2022 10:07:05 -0700 [thread overview]
Message-ID: <CAAPL-u80BFYTKK=0HRBXOeDTULyPOtbgu5V3fEYDOczTMxgJ1g@mail.gmail.com> (raw)
In-Reply-To: <68333b21a58604f3fd0e660f1a39921ae22849d8.camel@intel.com>
On Wed, May 11, 2022 at 12:49 AM ying.huang@intel.com
<ying.huang@intel.com> wrote:
>
> On Tue, 2022-05-10 at 22:30 -0700, Wei Xu wrote:
> > On Tue, May 10, 2022 at 4:38 AM Aneesh Kumar K.V
> > <aneesh.kumar@linux.ibm.com> wrote:
> > >
> > > Alistair Popple <apopple@nvidia.com> writes:
> > >
> > > > Wei Xu <weixugc@google.com> writes:
> > > >
> > > > > On Thu, May 5, 2022 at 5:19 PM Alistair Popple <apopple@nvidia.com> wrote:
> > > > > >
> > > > > > Wei Xu <weixugc@google.com> writes:
> > > > > >
> > > > > > [...]
> > > > > >
> > > > > > > > >
> > > > > > > > >
> > > > > > > > > Tiering Hierarchy Initialization
> > > > > > > > > `=============================='
> > > > > > > > >
> > > > > > > > > By default, all memory nodes are in the top tier (N_TOPTIER_MEMORY).
> > > > > > > > >
> > > > > > > > > A device driver can remove its memory nodes from the top tier, e.g.
> > > > > > > > > a dax driver can remove PMEM nodes from the top tier.
> > > > > > > >
> > > > > > > > With the topology built by firmware we should not need this.
> > > > > >
> > > > > > I agree that in an ideal world the hierarchy should be built by firmware based
> > > > > > on something like the HMAT. But I also think being able to override this will be
> > > > > > useful in getting there. Therefore a way of overriding the generated hierarchy
> > > > > > would be good, either via sysfs or kernel boot parameter if we don't want to
> > > > > > commit to a particular user interface now.
> > > > > >
> > > > > > However I'm less sure letting device-drivers override this is a good idea. How
> > > > > > for example would a GPU driver make sure it's node is in the top tier? By moving
> > > > > > every node that the driver does not know about out of N_TOPTIER_MEMORY? That
> > > > > > could get messy if say there were two drivers both of which wanted their node to
> > > > > > be in the top tier.
> > > > >
> > > > > The suggestion is to allow a device driver to opt out its memory
> > > > > devices from the top-tier, not the other way around.
> > > >
> > > > So how would demotion work in the case of accelerators then? In that
> > > > case we would want GPU memory to demote to DRAM, but that won't happen
> > > > if both DRAM and GPU memory are in N_TOPTIER_MEMORY and it seems the
> > > > only override available with this proposal would move GPU memory into a
> > > > lower tier, which is the opposite of what's needed there.
> > >
> > > How about we do 3 tiers now. dax kmem devices can be registered to
> > > tier 3. By default all numa nodes can be registered at tier 2 and HBM or
> > > GPU can be enabled to register at tier 1. ?
> >
> > This makes sense. I will send an updated RFC based on the discussions so far.
>
> Are these tier number fixed? If so, it appears strange that the
> smallest tier number is 0 on some machines, but 1 on some other
> machines.
When the kernel is configured to allow 3 tiers, we can always show all
the 3 tiers. It is just that some tiers (e.g. tier 0) may be empty on
some machines.
BTW, the userspace should not assume a specific meaning of a
particular tier id because it can change depending on the number of
tiers that the kernel is configured with. For example, the userspace
should not assume that tier-2 always means PMEM nodes. In a system
with 4 tiers, PMEM nodes may be in tier-3, not tier-2.
> Best Regards,
> Huang, Ying
>
>
next prev parent reply other threads:[~2022-05-11 17:07 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-30 2:10 RFC: Memory Tiering Kernel Interfaces Wei Xu
2022-04-30 3:59 ` Yang Shi
2022-04-30 6:37 ` Wei Xu
2022-05-06 0:01 ` Alistair Popple
2022-05-10 4:32 ` Wei Xu
2022-05-10 5:37 ` Alistair Popple
2022-05-10 11:38 ` Aneesh Kumar K.V
2022-05-11 5:30 ` Wei Xu
2022-05-11 7:34 ` Alistair Popple
2022-05-11 7:49 ` ying.huang
2022-05-11 17:07 ` Wei Xu [this message]
2022-05-12 1:42 ` ying.huang
2022-05-12 2:39 ` Wei Xu
2022-05-12 3:13 ` ying.huang
2022-05-12 3:37 ` Wei Xu
2022-05-12 6:24 ` Wei Xu
2022-05-06 18:56 ` Yang Shi
2022-05-09 14:32 ` Hesham Almatary
2022-05-10 3:24 ` Yang Shi
2022-05-10 9:59 ` Hesham Almatary
2022-05-10 12:10 ` Aneesh Kumar K V
2022-05-11 5:42 ` Wei Xu
2022-05-11 7:12 ` Alistair Popple
2022-05-11 9:05 ` Hesham Almatary
2022-05-12 3:02 ` ying.huang
2022-05-12 4:40 ` Aneesh Kumar K V
2022-05-12 4:49 ` Wei Xu
2022-05-10 4:22 ` Wei Xu
2022-05-10 10:01 ` Hesham Almatary
2022-05-10 11:44 ` Aneesh Kumar K.V
2022-05-01 18:35 ` Dan Williams
2022-05-03 6:36 ` Wei Xu
2022-05-06 19:05 ` Yang Shi
2022-05-07 7:56 ` ying.huang
2022-05-01 17:58 ` Davidlohr Bueso
2022-05-02 1:04 ` David Rientjes
2022-05-02 7:23 ` Aneesh Kumar K.V
2022-05-03 2:07 ` Baolin Wang
2022-05-03 6:06 ` Wei Xu
2022-05-03 17:14 ` Alistair Popple
2022-05-03 17:47 ` Dave Hansen
2022-05-03 22:35 ` Alistair Popple
2022-05-03 23:54 ` Dave Hansen
2022-05-04 1:31 ` Wei Xu
2022-05-04 17:02 ` Dave Hansen
2022-05-05 6:35 ` Wei Xu
2022-05-05 14:24 ` Dave Hansen
2022-05-10 4:43 ` Wei Xu
2022-05-02 6:25 ` Aneesh Kumar K.V
2022-05-03 7:02 ` Wei Xu
2022-05-02 15:20 ` Dave Hansen
2022-05-03 7:19 ` Wei Xu
2022-05-03 19:12 ` Tim Chen
2022-05-05 7:02 ` Wei Xu
2022-05-05 8:57 ` ying.huang
2022-05-05 23:57 ` Alistair Popple
2022-05-06 0:25 ` Alistair Popple
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