IBM Spectrum Scale: Dynamic page pool feature is available as Technical Preview in Spectrum Scale 5.1.7 and 5.1.8

Content

Overview

The dynamic page pool feature introduces the ability for Spectrum Scale to manage the page pool size within a range. Using the dynamic page pool feature avoids the administrative task of determining a fixed page pool size and allows better handling of workloads with varying memory usage requirements. This feature is available as Technical Preview in Spectrum Scale 5.1.7 and 5.1.8. The dynamic page pool feature must not be used in production environments during the Technical Preview; it is intended for test environments only. Also, review the restrictions and known issues section.

Consider participating in the Technical Preview and contact scale@us.ibm.com to sign up.

With the release of Spectrum Scale 5.1.8, this release is recommended for technical preview testing of the dynamic pagepool, since it includes important fixes.

Configuration

The default configuration is to use the static page pool as it is already available. Only this mode is supported for production workloads during the Technical Preview.

To enable the dynamic page pool feature on a node, apply the following configuration changes to that node, and restart Spectrum Scale. If the page pool configuration parameter is set to an explicit value, it is recommended to reset it back to the default:

mmchconfig dynamicPagepoolEnabled=yes -N node1
mmchconfig pagepool=default -N node1
mmshutdown -N node1
mmstartup -N node1

The dynamic page pool feature automatically adjusts the size of the page pool within the allowed range. The default minimum of the range for the dynamic page pool is 5 percent of the physical memory; the default for the maximum is 75 percent. The intent is that this default configuration is useful for a wide variety of use cases. If the default range does not work well, it can be changed through the configuration parameters pagepoolMinPhysMemPct and pagepoolMaxPhysMemPct. A restart of Spectrum Scale is also required for these parameters to take effect:

mmchconfig pagepoolMinPhysMemPct=10 -N node1
mmchconfig pagepoolMaxPhysMemPct=60 -N node1
mmshutdown -N node1
mmstartup -N node1

Usage

The allowed range of dynamic page pool and the current size can be queried through:

mmdiag --pagepool
mmdiag --pagepool -Y

Restrictions

• The dynamic page pool feature is only supported on Linux nodes.
• Changing the config parameters dynamicPagepoolEnabled, pagepoolMinPhysMemPct and pagepoolMaxPhysMemPct requires a restart of the daemon to become effective.
• The dynamic page pool feature cannot be used on NSD or ECE server nodes. This restriction is not automatically enforced during the Technical Preview. The administrator is responsible for enabling the dynamic page pool only on NSD client nodes. The plan is to enforce this restriction automatically when the feature becomes generally available.
• File system check (fsck) might fail when the current size of the dynamic page pool is not near the maximum size. The suggestion for the Technical Preview is to limit fsck to nodes without the dynamic page pool enabled. The plan is to implement proper co-existence for fsck and the dynamic page pool when the feature becomes generally available.
• The dynamic page pool Technical Preview is not supported together with RDMA. Ensure that RDMA is not enabled for the nodes with the dynamic page pool enabled. The plan is to support RDMA also on nodes with the dynamic page pool when the feature becomes generally available.