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8.16.3 Disadvantages of a Larger Maximum Page Size


8.16.3 Disadvantages of a Larger Maximum Page Size
A larger than standard value for the maximum page size can adversely affect the success rate of live migration of a logical domain, live migration of an Oracle Solaris kernel zone on a logical domain, and the PPAR DR operation by the deleteboard command.
We recommend setting the maximum page size to 256 MB to ensure the highest success rate for live migration of logical domains and Oracle Solaris kernel zones and in the PPAR DR operation by the deleteboard command. For details, see the descriptions below.
Success Rate of Live Migration and the PPAR DR Operation by the deleteboard Command
The success rate of live migration and the PPAR DR operation done by the deleteboard command depends on the memory usage at the destination.
Memory alignment for logical domains is constrained to multiples of the maximum page size. If the boundaries of the free contiguous memory region at the destination are not multiples of the maximum page size, the memory move fails.
Examples of Memory Usage at the Destination and the Effect of Large Maximum Page Sizes
Figure 8-8 shows an example of moving memory when the maximum page size of the logical domain is set to 2 GB. Even though there is a free contiguous memory region of 2 GB at the destination, the memory move fails because the boundaries of the free contiguous memory region are not multiples of the maximum page size.
Figure 8-8  When the Maximum Page Size of a Logical Domain Is Set to 2 GB
Figure 8-8  When the Maximum Page Size of a Logical Domain Is Set to 2 GB
Figure 8-9 shows an example of moving memory when the maximum page size of the logical domain is set to 256 MB. The memory move succeeds because the boundaries of the free memory region at the destination can be set to multiples of 256 MB.
Figure 8-9  When the Maximum Page Size of a Logical Domain Is Set to 256 MB
Figure 8-9  When the Maximum Page Size of a Logical Domain Is Set to 256 MB