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  • 1.  VMM Page Replacement in AIX 6.1 - 64k pool

    Posted Wed March 31, 2010 11:08 AM
    Reply

    Originally posted by: The_Doctor


    Environment --> Power6 Blade - 12 GB - AIX 6.1.4.0

    During periods of high user activity I noticed that VMM is scanning / freeing pages at a fairly high rate. Nothing unusual there, BUT I also noticed that VMM is maintaining 2 pools - a 4K and a 64K page pool.

    Further analysis shows that VMM page replacement scanning is almost 100% on the 4K pool.... while the activity on the 64K pool is pretty much idle. Here's 2 snippets taken with vmstat -P 4K 1 60 & vmstat -P 64K 1 60:
    
pgsz            memory                           page                   time ----- -------------------------- ------------------------------------ -------- siz      avm      fre    re    pi    po    fr     sr    cy hr mi se   4K  2461504  2087767     1154     0     0     0   105  20915     0 09:44:19 4K  2461504  2087767     1096     0     0     0   807  20675     0 09:44:20 4K  2461504  2087765     1104     0     0     0   845   5868     0 09:44:21 4K  2461504  2087764     1167     0     0     0  1060   2914     0 09:44:22 4K  2461504  2087764     1210     0     0     0  2018  14674     0 09:44:23 4K  2461504  2087765     1198     0     0     0  4589  18238     0 09:44:24 4K  2461504  2087764     1159     0     0     0 15054  15060     0 09:44:25 4K  2461504  2087764     1092     0     0     0 15427  15637     0 09:44:26 4K  2461504  2087764     1131     0     0     0  4625   4791     0 09:44:27 4K  2461504  2087764     1108     0     0     0  6497   7654     0 09:44:28 4K  2461504  2087765     1119     0     0     0  3086   3152     0 09:44:29 4K  2461504  2087764     1195     0     0     0  6588   9120     0 09:44:30 4K  2461504  2087771     1193     0     0     0  9389  14388     0 09:44:31 4K  2461504  2087843     1120     0     0     0  9320  12061     0 09:44:32 4K  2461504  2087841     1182     0     0     0 11267  11410     0 09:44:33 4K  2461504  2087842     1129     0     0     0  1094   1135     0 09:44:34 4K  2461504  2087841     1096     0     0     0  3400   5230     0 09:44:35 4K  2461504  2087869     1169     0     0     0  5706   9106     0 09:44:36 4K  2461504  2087870     1092     0     0     0  4349   5438     0 09:44:37 4K  2461504  2087871     1198     0     0     0  4357   5535     0 09:44:38   pgsz            memory                           page                   time ----- -------------------------- ------------------------------------ -------- siz      avm      fre    re    pi    po    fr     sr    cy hr mi se 64K    42764    40714     2050     0     0     0     0      0     0 09:44:19 64K    42764    40714     2050     0     0     0     0      0     0 09:44:20 64K    42764    40714     2050     0     0     0     0      0     0 09:44:21 64K    42764    40712     2052     0     0     0     0      0     0 09:44:22 64K    42764    40712     2052     0     0     0     0      0     0 09:44:23 64K    42764    40712     2052     0     0     0     0      0     0 09:44:24 64K    42764    40712     2052     0     0     0     0      0     0 09:44:25 64K    42764    40712     2052     0     0     0     0      0     0 09:44:26 64K    42764    40712     2052     0     0     0     0      0     0 09:44:27 64K    42764 40712     2052     0     0     0     0      0     0 09:44:28 64K    42764    40712     2052     0     0     0     0      0     0 09:44:29 64K    42764    40712     2052     0     0     0     0      0     0 09:44:30 64K    42764    40712     2052     0     0     0     0      0     0 09:44:31 64K    42764    40712     2052     0     0     0     0      0     0 09:44:32 64K    42764    40712     2052     0     0     0     0      0     0 09:44:33 64K    42764    40712     2052     0     0     0     0      0     0 09:44:34 64K    42764    40712     2052     0     0     0     0      0     0 09:44:35 64K    42764    40712     2052     0     0     0     0      0     0 09:44:36 64K    42764    40712     2052     0     0     0     0      0     0 09:44:37 64K    42764    40712     2052     0     0     0     0      0     0 09:44:38


    Similar samples have been taken on other days.... all showing the same thing. VMM is maintaining the 4K pool, business as usual, based on my default minfree 960, maxfree 1088, minperm% 3%, maxperm% 90%, and maxclient 90%. No problem on the 4K pool, VMM is doing it's job.

    But VMM also seems to be maintaining approx. 2000 free pages in the 64K pool..... in my case, that's about 128MB free in the 64K pool that is sledom used.

    So my question(s) are:

    1. is there a way to influence AIX 6.1 to dynamically move more free 64K pages to the 4K pool where I need them ?
    2. is there a whitepaper / redpaper that describes the dynamics of the 64K pool in AIX 6.1 ? and can you provide a link ? I have found good papers on VMM just not one that descibes the dynamics built into the 64K pool.

    And finally, yes, there seems there's a way to turn off the 64K pool.... e.g. vmo -o vmm_mpsize_support=0 (default is 2) but the 64K pool seems like a good thing so I'd rather not just turn it off.


  • 2.  Re: VMM Page Replacement in AIX 6.1 - 64k pool

    Posted Thu April 01, 2010 08:16 AM
    Reply

    Originally posted by: MarkTaylor


    Ref: http://www-03.ibm.com/systems/resources/systems_p_os_aix_whitepapers_multiple_page.pdf

    64KB Page Size Support
    On POWER5+ systems, AIX 5L Version 5.3 with the 5300-04 Recommended
    Maintenance Package supports a new 64KB page size when running the 64-bit kernel.
    AIX 5L has rich support around 64KB pages, and 64KB pages are intended to be generalpurpose.
    64KB pages are very easy to use, and it is expected that many applications will
    see performance benefits when using 64KB pages rather than 4KB pages.
    No system configuration changes are necessary to enable a system to use 64KB
    pages. On systems that support 64KB pages, the AIX 5L kernel will automatically
    configure 64KB pages for the system. 64KB pages are fully pageable, and the size of the
    pool of 64KB page frames on a system is dynamic and fully managed by AIX 5L.
    AIX 5L will vary the number of 4KB and 64KB page frames on a system to meet
    demand on the different page sizes. Both the svmon and vmstat commands can be used
    to monitor the number of 4KB and 64KB page frames on a system.

    Its dynamic, you would not want to touch it ..

    HTH
    Mark Taylor


  • 3.  Re: VMM Page Replacement in AIX 6.1 - 64k pool

    Posted Sun April 04, 2010 11:12 PM
    Reply

    Originally posted by: The_Doctor


    Thx Mark, that link was quite useful.

    Dunno why I didn't turn up that whitepaper before. With the right search arguments, google popped it right up.