Values for minperm and maxperm parameters
The operating system takes advantage of the varying requirements for real memory by leaving in memory pages of files that have been read or written.
If the file pages are requested again before their page frames are reassigned, this technique saves an I/O operation. These file pages may be from local or remote (for example, NFS) file systems.
The ratio of page frames used for files versus those used for computational (working or program text) segments is loosely controlled by the minperm and maxperm values:
- If percentage of RAM occupied by file pages falls below minperm, page-replacement steals both file and computational pages.
- If percentage of RAM occupied by file pages is between minperm and maxperm, page-replacement steals only file pages.
In a particular workload, it might be worthwhile to emphasize the
avoidance of file I/O. In another workload, keeping computational
segment pages in memory might be more important. To understand what
the ratio is in the untuned state, use the vmstat command
with the -v option.
# vmstat -v
1048576 memory pages
936784 lruable pages
683159 free pages
1 memory pools
267588 pinned pages
90.0 maxpin percentage
3.0 minperm percentage
90.0 maxperm percentage
5.6 numperm percentage
52533 file pages
0.0 compressed percentage
0 compressed pages
5.6 numclient percentage
90.0 maxclient percentage
52533 client pages
0 remote pageouts scheduled
0 pending disk I/Os blocked with no pbuf
0 paging space I/Os blocked with no psbuf
2228 filesystem I/Os blocked with no fsbuf
31 client filesystem I/Os blocked with no fsbuf
0 external pager filesystem I/Os blocked with no fsbuf
29.8 percentage of memory used for computational pages The numperm percentage value shows the percentage of real memory used by file segments. The value 5.6% corresponds to 52533 file pages in memory.