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Operating Systems AIX AIX understanding memory using Post 303037086 by bakunin on Tuesday 23rd of July 2019 05:23:40 AM
Old 07-23-2019
Quote:
Originally Posted by Phat
I would like to understand better in AIX memory use
Basically you have three types of memory in an AIX system: "used" and "unused" and the "used" category divides into two parts: "computational" and "file" memory.

"unused" is memory the kernel has absolutely no use for. In a longer running (and correctly tuned) system this is near to zero.

"computational" memory is the memory used by loaded and running programs.

"file" memory is basically cache. All the memory not used for programs (but not strictly set aside by tuning provisions) is added to the file cache - over time. The kernel will only make use of memory to cache file access if it has an idea what to cache. This is why freshly started systems have lots of free memory. The kernel simply doesn't know what to put into the cache and therefore doesn't allocate a lot of it.

Should RAM become used over time and more computational memory is needed (i.e. more programs are started) the file cache is diminished accordingly or regrown again should memory become free again. The tuning parameters "numperm", "minperm", "maxperm", "minclient" and "maxclient" deal with how and when exactly file memory is turned into computational memory and vice versa. There is a daemon - the "least recently used daemon" or "lrud" for short - which constantly scans memory pages and decides when they should be claimed as "computational" or "file". What it is doing exactly shows in the output of vmstat -vs, i.e. "revolutions of the clock hand" means: since the last start the lrud has scanned the whole memory that often completely. If this value is fast growing you know that even if memory is not scarce right now it is at the brink of being exhausted and paging will start soon if any more memory is needed.

You may want to consult my "Most Incomplete Guide to Performance Tuning" for a more thorough (though not complete - this is a complex area) discussion about memory management in UNIX systems in general and how to assess it.

I hope this helps.

bakunin
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Acme::Brainfuck(3)					User Contributed Perl Documentation					Acme::Brainfuck(3)

NAME
Acme::Brainfuck - Embed Brainfuck in your perl code SYNOPSIS
#!/usr/bin/env perl use Acme::Brainfuck; print 'Hello world!', chr ++++++++++. ; DESCRIPTION
Brainfuck is about the tiniest Turing-complete programming language you can get. A language is Turing-complete if it can model the opera- tions of a Turing machine--an abstract model of a computer defined by the British mathematician Alan Turing in 1936. A Turing machine con- sists only of an endless sequence of memory cells and a pointer to one particular memory cell. Yet it is theoretically capable of perform- ing any computation. With this module, you can embed Brainfuck instructions delimited by whitespace into your perl code. It will be trans- lated into Perl as parsed. Brainfuck has just just 8 instructions (well more in this implementation, see "Extensions to ANSI Brainfuck" below.) which are as follows Instructions + Increment Increase the value of the current memory cell by one. - Decrement Decrease the value of the current memory cell by one. > Forward Move the pointer to the next memory cell. < Back Move the pointer to the previous memory cell. , Input Read a byte from Standard Input and store it in the current memory cell. . Output Write the value of the current memory cell to standard output. [ Loop If the value of the current memory cell is 0, continue to the cell after the next ']'. ] Next Go back to the last previous '['. Extensions to ANSI Brainfuck This implementation has extra instructions available. In order to avoid such terrible bloat, they are only available if you use the ver- bose pragma like so: use Acme::Brainfuck qw/verbose/; The extra instructions are: ~ Reset Resets the pointer to the first memory cell and clear all memory cells. # Peek Prints the values of the memory pointer and the current memory cell to STDERR. See also "Debugging" below. Debugging By using the debug pragma like this: use Acme::Brainfuck qw/debug/; you can dump out the generated perl code. (Caution: it is not pretty.) The key to understanding it is that the memory pointer is repre- sented by $p, and the memory array by @m Therefore the value of the current memory cell is $m[$p]. RETURN VALUE
Each sequence of Brainfuck instructions becomes a Perl block and returns the value of the current memory cell. EXAMPLES
JABH #!/usr/bin/env perl use Acme::Brainfuck; print "Just another "; ++++++[>++++++++++++++++<-]> ++.-- >+++[<++++++>-]<.>[-]+++[<------>-]< +.- +++++++++.--------- ++++++++++++++.-------------- ++++++.------ >+++[<+++++++>-]<.>[-]+++[<------->-]< +++.--- +++++++++++.----------- print " hacker. "; Countdown #!/usr/bin/env perl use strict; use Acme::Brainfuck qw/verbose/; print "Countdown commencing... "; ++++++++++[>+>+<<-] >>+++++++++++++++++++++++++++++++++++++++++++++++<< ++++++++++[>>.-<.<-] print "We have liftoff! "; Reverse #!/usr/bin/env perl use Acme::Brainfuck qw/verbose/; while(1) { print "Say something to Backwards Man and then press enter: "; +[->,----------]< print 'Backwards Man says, "'; [+++++++++++.<]< print "" to you too. "; ~ } Math #!/usr/bin/env perl use Acme::Brainfuck; use strict; use warnings; my $answer = +++[>++++++<-]> ; print "3 * 6 = $answer "; VERSION
1.1.1 Apr 06, 2004 AUTHOR
Jaldhar H. Vyas E<lt>jaldhar@braincells.comE<gt> THANKS
Urban Mueller - The inventor of Brainfuck. Damian Conway - For twisting perl to hitherto unimaginable heights of weirdness. Marco Nippula <http://www.hut.fi/~mnippula/> - Some code in this module comes from his brainfuck.pl Mr. Rock - Who has a nice Brainfuck tutorial at <http://www.cydathria.com/bf/>. Some of the example code comes from there. COPYRIGHT AND LICENSE
Copyright (c) 2004, Consolidated Braincells Inc. Licensed with no warranties under the Crowley Public License: "Do what thou wilt shall be the whole of the license." perl v5.8.3 2004-04-06 Acme::Brainfuck(3)
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