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1 reply Latest Post - ‏2010-05-05T21:40:56Z by SystemAdmin
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Pinned topic Determining page sizes on Linux on Power

‏2010-05-05T21:30:17Z |
On SLES 11 on POWER7, I prefer the page size of 64K - AIX's medium page.

cat /proc/meminfo shows hugepagesize of 16MB, but no allocation.
So, I assume that this is not set up for Huge page.

Can you tell me what the page size is then ? I thought the default is 4KB ( small page size).
How are medium pages (64K) set up ?
Updated on 2010-05-05T21:40:56Z at 2010-05-05T21:40:56Z by SystemAdmin
  • SystemAdmin
    SystemAdmin
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    Re: Determining page sizes on Linux on Power

    ‏2010-05-05T21:40:56Z  in response to null
    The newer distros (RHEL 5 and SLES 11) "come with" the default page size of 64KB. Nothing to do - it's just there.

    The way to easily check this is with the /usr/bin/time command using the verbose flag -v (but of course, where else would they put that?)
    
    /usr/bin/time -v sleep 0  2>&1 | grep Page Page size (bytes): 65536
    

    The 16MB pages are controlled separately with packages like libhugetlbfs. The Linux kernel is enabled for 16MB pages (huge pages in Linux terminology), but there are things you would need to do to exploit that.

    For what its worth, the Linux kernel can be built with either 4KB pages or with 64KB pages. The Linux community has not implemented a simultaneous multi-page kernel - it's an either/or build process. The 64KB pages were overall deemed more applicable and a better fit for the POWER systems. That said, there are cases where this will make Linux on POWER an inappropriate server solution - in particular in cases where many many small files are used, which would obviously waste a lot of memory.