My Oracle Support Banner

Exalogic Virtual Steps To Increase SWIOTLB Buffer Size To 512MB On Dom0 Compute Nodes (Doc ID 2593092.1)

Last updated on JULY 27, 2022

Applies to:

Oracle Exalogic Elastic Cloud Software - Version and later
Linux x86-64
Oracle Virtual Server x86-64

**** Steps in this MOS Note only applies to Exalogic Virtual releases *****


This MOS Note provides detailed steps to increase swiotlb setting on Exalogic Virtual rack Dom0 compute nodes.

In Exalogic Virtual rakcks IB networks on the Guest VMs on Dom0 compute nodes and in some cases Dom0 compute nodes itself do not work as expected if there is exhaustion of resources in Software Input Output Translation Lookaside Buffer (swiotlb). swiotlb is an IO memory management function of the Linux kernel used by the XEN hypervisor and OVS Networking stack. In Exalogic we have default swiotlb setting of 256MB. In Exalogic releases which has UEK4 based kernel swiotlb buffer size of 256MB may not be enough if there are more number of VM's or large VM's configured or if there is significant network IO in the rack.


  1. Procedure in this MOS note to increase SWIOTLB buffer size has to be done during Maintenance window as it involves rebooting the OVS Dom0 Compute nodes. For rebooting Dom0 Compute nodes reboot, All the VMs running on Dom0 compute node (which hosts Applications) have to be brought down. So maintenance window has to be scheduled for implementing the procedure in this MOS note.

  2. The default swiotlb setting has been increased to 512 MB in Jan 2020 PSU (and higher). If you continue to encounter swiotlb buffer full issue, swiotlb has to be increased to 768 MB. Please reach out to Oracle Exalogic Support by opening Service Request for assistance in increasing the swiotlb setting to 768 MB.



To view full details, sign in with your My Oracle Support account.

Don't have a My Oracle Support account? Click to get started!

In this Document
 swiotlb change on one compute node at a time (non dcli method)
 DCLI method to make swiotlb changes on all or multiple compute nodes at a time

My Oracle Support provides customers with access to over a million knowledge articles and a vibrant support community of peers and Oracle experts.