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Full Discussion: AIX 6.1 memory tuning
Operating Systems AIX AIX 6.1 memory tuning Post 302887193 by -=XrAy=- on Thursday 6th of February 2014 09:09:48 AM
Old 02-06-2014
Quote:
Originally Posted by dzodzo
How can i tell what will be the maximum kernel memory? We measured this after reboot and starting the applications, kernel took only 2 GB but during 4 months it gradually grew to 13 GB. What would happen if i configured applications to take let's say 60 GB of memory. Will AIX handle that and live with 4 GB for kernel or will it start trashing until reboot is necessary?

I do not know a formula too calculate the minimum for kernel memory.
As you said the memory usage will grow with time and usage (mbufs, inode cache, jfs bufstructs, etc.) and the increase depends on the maximum installed memory. The Kernel used pinned memory (vmstat -v) and if your application with 60GB also used pinned memory, your server will crash/panic if there are no more memory which can be pinned. That happened to us after two weeks with a wrong Informix memory configuration. The other way the server starts to swap out (paging space) and the performance slows down.

Regards
 

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ncsize(5)							File Formats Manual							 ncsize(5)

NAME
ncsize - number of Directory Name Lookup Cache (DNLC) entries VALUES
Failsafe Default Allowed values The minimum value allowed is The maximum value allowed is memory limited. The value is further constrained in that it must be equal to or greater than eight times the value of the number of locks for the DNLC Specify a positive integer value. DESCRIPTION
To speed up the search through directories in the kernel, there is a memory resident cache of directories called the During a filename lookup in the kernel, any directories or files encountered are retained in the DNLC for future reference. The tunable dictates the number of entries in the DNLC, which is statically allocated at system boot time. Therefore, the larger the value of the larger the number of directory/file entries that can be kept cached in memory for filename lookup. Who Is Expected to Change This Tunable? HP-UX system administrators. Restrictions on Changing This tunable is static. Any changes to the value of this tunable will require system reboot before taking effect. When Should the Value of This Tunable Be Raised? The value may need to be raised to improve filename lookup performance when running applications which require large numbers of filename access. What are the Side Effects of Raising the Value? More system memory will be consumed for the DNLC. When Should the Value of This Tunable Be Lowered? The value can be lowered to limit the number of entries in the DNLC and reduce memory consumption. What are the Side Effects of Lowering the Value? Less system memory will be consumed for the DNLC upon system reboot. Operations requiring filename lookup (e.g. open(2)) may experience performance degradation. What Other Tunable Values Should Be Changed at the Same Time? The value of must be equal to or greater than eight times the value of WARNINGS
All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its meaning changed in future releases of HP-UX. Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parameter values. After installation, some tunable parameters may no longer be at the default or recommended values. For information about the effects of installation on tun- able values, consult the documentation for the kernel software being installed. For information about optional kernel software that was factory installed on your system, see at AUTHOR
was developed by HP. SEE ALSO
kctune(1M), sam(1M), gettune(2), settune(2), dnlc_hash_locks(5). Tunable Kernel Parameters ncsize(5)
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