On 6/8/22 11:46 PM, Johannes Weiner wrote:
On Wed, Jun 08, 2022 at 09:43:52PM +0530, Aneesh Kumar K V wrote:
On 6/8/22 9:25 PM, Johannes Weiner wrote:
Hello,
On Wed, Jun 08, 2022 at 10:11:31AM -0400, Johannes Weiner wrote:
On Fri, Jun 03, 2022 at 07:12:29PM +0530, Aneesh Kumar K.V wrote:
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_MEMORY_TIERS_H
+#define _LINUX_MEMORY_TIERS_H
+
+#ifdef CONFIG_TIERED_MEMORY
+
+#define MEMORY_TIER_HBM_GPU 0
+#define MEMORY_TIER_DRAM 1
+#define MEMORY_TIER_PMEM 2
+
+#define MEMORY_RANK_HBM_GPU 300
+#define MEMORY_RANK_DRAM 200
+#define MEMORY_RANK_PMEM 100
+
+#define DEFAULT_MEMORY_TIER MEMORY_TIER_DRAM
+#define MAX_MEMORY_TIERS 3
I understand the names are somewhat arbitrary, and the tier ID space
can be expanded down the line by bumping MAX_MEMORY_TIERS.
But starting out with a packed ID space can get quite awkward for
users when new tiers - especially intermediate tiers - show up in
existing configurations. I mentioned in the other email that DRAM !=
DRAM, so new tiers seem inevitable already.
It could make sense to start with a bigger address space and spread
out the list of kernel default tiers a bit within it:
MEMORY_TIER_GPU 0
MEMORY_TIER_DRAM 10
MEMORY_TIER_PMEM 20
Forgive me if I'm asking a question that has been answered. I went
back to earlier threads and couldn't work it out - maybe there were
some off-list discussions? Anyway...
Why is there a distinction between tier ID and rank? I undestand that
rank was added because tier IDs were too few. But if rank determines
ordering, what is the use of a separate tier ID? IOW, why not make the
tier ID space wider and have the kernel pick a few spread out defaults
based on known hardware, with plenty of headroom to be future proof.
$ ls tiers
100 # DEFAULT_TIER
$ cat tiers/100/nodelist
0-1 # conventional numa nodes
<pmem is onlined>
$ grep . tiers/*/nodelist
tiers/100/nodelist:0-1 # conventional numa
tiers/200/nodelist:2 # pmem
$ grep . nodes/*/tier
nodes/0/tier:100
nodes/1/tier:100
nodes/2/tier:200
<unknown device is online as node 3, defaults to 100>
$ grep . tiers/*/nodelist
tiers/100/nodelist:0-1,3
tiers/200/nodelist:2
$ echo 300 >nodes/3/tier
$ grep . tiers/*/nodelist
tiers/100/nodelist:0-1
tiers/200/nodelist:2
tiers/300/nodelist:3
$ echo 200 >nodes/3/tier
$ grep . tiers/*/nodelist
tiers/100/nodelist:0-1
tiers/200/nodelist:2-3
etc.
tier ID is also used as device id memtier.dev.id. It was discussed that we
would need the ability to change the rank value of a memory tier. If we make
rank value same as tier ID or tier device id, we will not be able to support
that.
Is the idea that you could change the rank of a collection of nodes in
one go? Rather than moving the nodes one by one into a new tier?
[ Sorry, I wasn't able to find this discussion. AFAICS the first
patches in RFC4 already had the struct device { .id = tier }
logic. Could you point me to it? In general it would be really
helpful to maintain summarized rationales for such decisions in the
coverletter to make sure things don't get lost over many, many
threads, conferences, and video calls. ]
Most of the discussion happened not int he patch review email threads.
RFC: Memory Tiering Kernel Interfaces (v2)
https://lore.kernel.org/linux-mm/CAAPL-u_diGYEb7+WsgqNBLRix-nRCk2SsDj6p9r8j5JZwOABZQ@xxxxxxxxxxxxxx
RFC: Memory Tiering Kernel Interfaces (v4)
https://lore.kernel.org/linux-mm/CAAPL-u9Wv+nH1VOZTj=9p9S70Y3Qz3+63EkqncRDdHfubsrjfw@xxxxxxxxxxxxxx
-aneesh
