Originally posted by: kah00na
On a busy Oracle AIX server, the lru daemon scans and free up a lot of pages a lot of the day. However, most of them seem to be persistent data (aka files). When persistent data is freed in memory, it does not go to the paging space, rather it is paged to the filesystem. You can see the "pages/sec to File System" in the memory section of nmon. It looks like this:
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pages/sec In Out
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to Paging Space 0.0 0.0
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to File System 606.5 1293.6
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Page Scans 1638.1
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Page Cycles 0.0
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Page Steals 1512.1
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Page Faults 18879.4
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Only the working storage (or "computational") pages go to the paging space. Therefore, when we see the paging space being used, it is because the computational pages are being freed from the memory and they go to the paging space. persistent data could still be in the process of being paged out, but since it goes to the filesystem, you don't see the paging space usage going up.
When would the system page out computational pages instead of files? That is dependent upon the minperm% and the maxperm%. If the lru_file_repage is set to "0", then the only time computational pages should be sent to the paging space is when the total number of free pages goes below the minperm%. With lru_file_repage set to 0, anytime the numperm% is ABOVE the minperm%, only file pages should be freed from memory. Once the system has less than the minperm% of free pages available, then the computational pages are just as likely to be paged out to memory as the file pages.
Run "svmon -G" and look at the "memory" row and "size" column. Take that number times your minperm% (1%). When the number of free pages goes below the resulting number, the working storage (aka computational pages) become candidates to be paged out to the paging space.
Assuming your memory/size field in "svmon -G" is 3670016, once the amount of "fre" column goes below 36,700.16 (3670016*0.01), computation pages can be sent to the paging space and probably are.
If the "fre" pages can be kept above that threshold, you "shouldn't" see any activity to the paging space. Review your vmstat files and see if the paging is occuring when your "fre" pages are less than that threshold. You may not actually see a lower number than the threshold because you are looking at averages and the lru is working to free up pages, but you can make a good guess that it is by subtracting the "fr"eed pages from the "fre" total.
This begs the question, how do you keep it below that threshold? You can try playing with the minfree/maxfree settings some. Perhaps spreading out the gap between them from 512 to 768. Maybe?
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