Section 5.17. Large Page Support

5.17. Large Page Support

Large page usage is primarily intended to provide performance improvements to high-performance computing (HPC) applications. Memory-access-intensive applications that use large amounts of virtual memory may obtain performance improvements by using large pages. The large page performance improvements are attributable to reduced translation lookaside buffer (TLB) misses due to the TLB being able to map a larger virtual memory range. Large pages also improve memory prefetching by eliminating the need to restart prefetch operations on 4KB boundaries.

In AIX, large page support^[22] for executables can be turned on in four ways:

^[22] AIX support for large pages, http://www-1.ibm.com/servers/aix/whitepapers/large_page.pdf

1. Through the compiler command

   $ xlC bmaxdata=0xXXXXXXXX 

2. Linker command

   $ ld blpdata o large_exec 

3. Through the ldedit command

   $ ldedit blpdata large_exec 

4. Environment variable

   $ export LDR_CNTRL=LARGE_PAGE_DATA=Y 

In Linux, you can enable large page support by reconfiguring the kernel or by using the traditional memory systems calls. Chapter 3 covers how to enable large page support for Linux in more detail.