[RFC PATCH 0/2] mm: mempolicy: Multi-tier interleaving

[Ravi Jonnalagadda <ravis.opensrc@micron.com>]

From: Ravi Shankar <ravis.opensrc@micron.com>

Hello,

The current interleave policy operates by interleaving page requests
among nodes defined in the memory policy. To accommodate the
introduction of memory tiers for various memory types (e.g., DDR, CXL,
HBM, PMEM, etc.), a mechanism is needed for interleaving page requests
across these memory types or tiers.

This can be achieved by implementing an interleaving method that
considers the tier weights.
The tier weight will determine the proportion of nodes to select from
those specified in the memory policy.
A tier weight can be assigned to each memory type within the system.

Hasan Al Maruf had put forth a proposal for interleaving between two
tiers, namely the top tier and the low tier. However, this patch was
not adopted due to constraints on the number of available tiers.

https://lore.kernel.org/linux-mm/YqD0%2FtzFwXvJ1gK6@cmpxchg.org/T/

New proposed changes:

1. Introducea sysfs entry to allow setting the interleave weight for each
memory tier.
2. Each tier with a default weight of 1, indicating a standard 1:1
proportion.
3. Distribute the weight of that tier in a uniform manner across all nodes.
4. Modifications to the existing interleaving algorithm to support the
implementation of multi-tier interleaving based on tier-weights.

This is inline with Huang, Ying's presentation in lpc22, 16th slide in
https://lpc.events/event/16/contributions/1209/attachments/1042/1995/\
Live%20In%20a%20World%20With%20Multiple%20Memory%20Types.pdf

Observed a significant increase (165%) in bandwidth utilization
with the newly proposed multi-tier interleaving compared to the
traditional 1:1 interleaving approach between DDR and CXL tier nodes,
where 85% of the bandwidth is allocated to DDR tier and 15% to CXL
tier with MLC -w2 option.

Usage Example:

1. Set weights for DDR (tier4) and CXL(teir22) tiers.
echo 85 > /sys/devices/virtual/memory_tiering/memory_tier4/interleave_weight
echo 15 > /sys/devices/virtual/memory_tiering/memory_tier22/interleave_weight

2. Interleave between DRR(tier4, node-0) and CXL (tier22, node-1) using numactl
numactl -i0,1 mlc --loaded_latency W2

Srinivasulu Thanneeru (2):
  memory tier: Introduce sysfs for tier interleave weights.
  mm: mempolicy: Interleave policy for tiered memory nodes

 include/linux/memory-tiers.h |  27 ++++++++-
 include/linux/sched.h        |   2 +
 mm/memory-tiers.c            |  67 +++++++++++++++-------
 mm/mempolicy.c               | 107 +++++++++++++++++++++++++++++++++--
 4 files changed, 174 insertions(+), 29 deletions(-)

-- 
2.39.3