Don't bother reading this any further if your only concern is a Linux based system. This tuning is only available for the Zaurus if running OpenBSD since sysctl is part of OpenBSD and the libc implementation is part of OpenBSD rather than using the GNU libc.
Now, before we go any further let me warn you that some of the tuning options that I suggest will actively disable some of the security features of OpenBSD related to guarding the system against buffer overrun exploits/stack smashing and encryption of the paging subsystem. If you want to retain your Zaurus in the most secure fashion then you should probably leave it at the default settings, however, most users will accept that tuning is based upon your use profile for the device.
The usage profile that I wanted to enhance was system performance when the system had become overburdened, particularly when running X and in my case XFCE4 which I love as a desktop environment. - To this end the settings are designed to improve system performance when memory utilisation is getting high, something that is likely to happen with most Zaurus users running OpenBSD.
The settings are quick to apply and require a reboot once applied, likewise they can be quickly removed and a reboot will clear them entirely.
sysctl settings
The OpenBSD Kernel can be tuned by various system settings directly through the program sysctl. If these settings are stored in /etc/sysctl.conf they will be implemented at boot time.
The following settings I am recommending should be changed or added in sysctl.conf
vm.swapencrypt.enable=0
This setting disables swap (page partition) encryption so should yield a performance boost when the system is overburdened at the cost of the potential ability to decode sensitive data stored in the page partition should the device fall into the wrong hands.
kern.stackgap_random=0
This parameter governs the size of the random amount of memory allocated to the stack during certain operations. The mechanism is there to stop predictable stack smashing exploits but can add a considerable amount of memory allocation to processes (hundreds of Kilobytes in some cases).
malloc settings
The memory allocation features within BSD (unlike Linux) are tuneable. They are implemented within /src/lib/libc/stdlib/malloc.c and it is only by understanding this file that an accurate assessment of the options can be made. The malloc man page lists all the settings, however, it does not go on to explain what 'Hinting' does etc.
The settings that I am going to recommend (see the malloc man page) are more fully explained as follows.
a = Don't cause Abort (core dumps on failures)
z = Turn off zeroing of pages, time consuming and with it turned on the J/j parameter is ignored! (need to read the source to see this)
j = Don't fill allocations with junk (our processor has enough to do already).
g = Don't allocate Guard Pages that waste our memory (security feature here)
p = Turn off pointer protection - again allocates more memory in each malloc/realloc call (this can skip some major options if left enabled such as the realloc stuff [R])
H = Turn on Hinting (unused pages are marked with MADV_FREE - see madvise man page, the kernel will therefore discard them rather than page them under low memory condition)
R = Turn on always realloc (reallocation to aid compacting performances). Applications such as AbiWord in particular that make significant use of heap space frequently realloc and will release pages more frequently.
The way to make these settings global is to create a symbolic link as follows...
ln -s 'azjgpHR' /etc/malloc.conf
Normally symlinks point to files, however, in this case libc reads the symlink directly for the options. This is a performance technique since the settings will be more directly cached for access than being stored within a file.
Notice that I don't make recommendations about the use of the < or > flags to reduce or increase the malloc cache size. With the useage profile that I have I have found no discernable benefit from changing it, however, you may wish to profile applications and daemons to discern an appropriate setting for yourself.
Note the settings will NOT work if you create a regular file called /etc/malloc.conf
Some stats
The real statistics behind this tuning will only become evident when we overload the Zaurus to the point that paging occurs.
The following 3 'top' snapshots were taken from an ssh connection to a Zaurus running full XFCE4 and AbiWord 2.4 with ispell dictionaries built in. Each snapshot represents a newly booted configuration.
Snapshot 1 - Default configuration + sysctl vm.swapencrypt=0
load averages: 0.66, 0.70, 0.41 21:49:43
29 processes: 28 idle, 1 on processor
CPU states: 10.8% user, 0.0% nice, 5.6% system, 0.0% interrupt, 83.6% idle
Memory: Real: 32M/57M act/tot Free: 888K Swap: 2304K/128M used/tot
PID USERNAME PRI NICE SIZE RES STATE WAIT TIME CPU COMMAND
31620 andrews 2 0 5472K 11M sleep poll 0:41 9.33% xfce4-panel
23208 andrews 2 0 8752K 15M sleep poll 0:24 5.27% AbiWord-2.4
12371 andrews 2 0 5864K 5424K sleep select 0:20 4.05% Xorg
8585 andrews 2 0 2280K 6476K sleep poll 0:06 0.00% xfdesktop
3123 andrews 2 0 1808K 6584K idle poll 0:05 0.00% xfwm4
32699 andrews 2 0 1852K 6948K idle poll 0:04 0.00% xftaskbar4
1088 andrews 2 0 624K 1532K sleep poll 0:03 0.00% xscreensaver
32600 andrews 2 0 856K 4424K idle poll 0:03 0.00% xfce4-session
26271 andrews 2 0 1500K 4724K sleep poll 0:02 0.00% xfce-mcs-mana
23507 root 2 0 688K 568K idle select 0:01 0.00% sshd
15707 root 2 0 3256K 720K idle netio 0:00 0.00% sshd
9959 andrews 28 0 524K 984K onproc - 0:00 0.00% top
15009 _syslogd 2 0 460K 496K idle poll 0:00 0.00% syslogd
27878 root 2 0 1140K 980K sleep select 0:00 0.00% sendmail
12721 andrews 2 0 3256K 1200K sleep select 0:00 0.00% sshd
5402 andrews 18 0 668K 8K idle pause 0:00 0.00% ksh
10667 andrews 10 0 472K 728K idle wait 0:00 0.00% xinit
32524 andrews 18 0 556K 8K idle pause 0:00 0.00% sh
13282 root 2 0 300K 452K idle kqread 0:00 0.00% apmd
4478 root 2 0 564K 596K idle select 0:00 0.00% cron
22154 root 3 0 224K 480K idle ttyin 0:00 0.00% getty
818 andrews 18 0 512K 8K idle pause 0:00 0.00% ksh
1 root 10 0 444K 8K idle wait 0:00 0.00% init
26439 root 2 0 312K 440K idle select 0:00 0.00% inetd
26977 root 2 0 432K 340K idle netio 0:00 0.00% syslogd
11796 root -6 0 148K 428K idle htplev 0:00 0.00% hotplugd
5010 andrews 2 0 2000K 392K idle netio 0:00 0.00% Xorg
15720 andrews 18 0 548K 8K idle pause 0:00 0.00% sh
20786 andrews 2 0 532K 444K idle select 0:00 0.00% ssh-agent
Snapshot 2 - After applying sysctl kern.stackgap_random = 0
Here we expect to see a random element removed from the memory allocation of the processes. The processes should show as smaller than the original but the amount is indeterminable due to the random amount of bloat imposed by the stackgap_random mechanism.
load averages: 0.74, 0.77, 0.39 21:59:28
29 processes: 3 running, 25 idle, 1 on processor
CPU states: 11.2% user, 0.0% nice, 4.7% system, 0.0% interrupt, 84.2% idle
Memory: Real: 32M/57M act/tot Free: 1172K Swap: 6592K/128M used/tot
PID USERNAME PRI NICE SIZE RES STATE WAIT TIME CPU COMMAND
3082 andrews 2 0 5240K 7792K run - 0:29 9.57% xfce4-panel
31372 andrews 28 0 8604K 15M run - 0:23 4.30% AbiWord-2.4
2484 andrews 2 0 5632K 5180K run - 0:15 3.27% Xorg
31105 andrews 2 0 2024K 5784K sleep poll 0:06 0.00% xfdesktop
31443 andrews 2 0 1756K 6472K idle poll 0:05 0.00% xfwm4
6667 andrews 2 0 1624K 6892K idle poll 0:05 0.00% xftaskbar4
22111 andrews 2 0 628K 1532K sleep poll 0:04 0.00% xscreensaver
5673 andrews 2 0 756K 4280K idle poll 0:03 0.00% xfce4-session
28783 andrews 2 0 1412K 4164K sleep poll 0:02 0.00% xfce-mcs-mana
1574 root 2 0 540K 416K idle select 0:01 0.00% sshd
29507 root 2 0 3148K 552K idle netio 0:00 0.00% sshd
825 andrews 28 0 388K 928K onproc - 0:00 0.00% top
2677 _syslogd 2 0 256K 472K idle poll 0:00 0.00% syslogd
13631 andrews 2 0 3160K 1032K sleep select 0:00 0.00% sshd
30489 root 2 0 1004K 952K sleep select 0:00 0.00% sendmail
14046 andrews 18 0 484K 8K idle pause 0:00 0.00% ksh
16693 andrews 10 0 220K 708K idle wait 0:00 0.00% xinit
3895 andrews 18 0 480K 8K idle pause 0:00 0.00% sh
2724 root 3 0 192K 452K idle ttyin 0:00 0.00% getty
22854 andrews 18 0 480K 8K idle pause 0:00 0.00% ksh
1 root 10 0 576K 8K idle wait 0:00 0.00% init
11291 root 2 0 232K 412K idle select 0:00 0.00% inetd
26294 root 2 0 408K 612K idle select 0:00 0.00% cron
19721 root 2 0 232K 312K idle netio 0:00 0.00% syslogd
4774 root 2 0 156K 424K idle kqread 0:00 0.00% apmd
20647 root -6 0 148K 400K idle htplev 0:00 0.00% hotplugd
18752 andrews 2 0 1772K 364K idle netio 0:00 0.00% Xorg
17329 andrews 2 0 276K 292K idle select 0:00 0.00% ssh-agent
797 andrews 18 0 472K 8K idle pause 0:00 0.00% sh
Snapshot 3 - After applying the /etc/malloc.conf tuning.
Now we expect to see less memory utilisation both in terms of process size and resident statistics for each of the XFCE4 processes. It it possible that AbiWord at this stage may use more memory since the operating system is free to give it.
load averages: 1.13, 0.92, 0.46 22:17:37
29 processes: 1 running, 27 idle, 1 on processor
CPU states: 14.3% user, 0.0% nice, 5.3% system, 0.0% interrupt, 80.4% idle
Memory: Real: 30M/56M act/tot Free: 2112K Swap: 4736K/128M used/tot
PID USERNAME PRI NICE SIZE RES STATE WAIT TIME CPU COMMAND
2201 andrews 2 0 8604K 14M sleep poll 0:25 32.86% AbiWord-2.4
15806 andrews 2 0 5244K 7628K run - 0:30 10.06% xfce4-panel
23689 andrews 2 0 5624K 5036K sleep select 0:17 8.25% Xorg
7526 andrews 2 0 1656K 6768K sleep poll 0:05 3.32% xftaskbar4
22566 andrews 2 0 1752K 6432K sleep poll 0:05 0.88% xfwm4
16586 andrews 2 0 608K 1516K sleep poll 0:05 0.49% xscreensaver
13100 andrews 2 0 2016K 5700K sleep poll 0:06 0.00% xfdesktop
31169 andrews 2 0 764K 4196K sleep poll 0:03 0.00% xfce4-session
20358 andrews 2 0 1384K 4128K sleep poll 0:02 0.00% xfce-mcs-mana
27366 root 2 0 540K 444K idle select 0:01 0.00% sshd
7761 root 2 0 3168K 584K idle netio 0:00 0.00% sshd
28565 andrews 28 0 392K 956K onproc - 0:00 0.00% top
12637 andrews 2 0 3168K 1056K sleep select 0:00 0.00% sshd
18604 _syslogd 2 0 268K 496K sleep poll 0:00 0.00% syslogd
128 andrews 18 0 484K 8K idle pause 0:00 0.00% ksh
21710 root 2 0 996K 980K sleep select 0:00 0.00% sendmail
14304 andrews 10 0 212K 732K idle wait 0:00 0.00% xinit
13362 andrews 18 0 476K 8K idle pause 0:00 0.00% sh
13211 root 2 0 408K 636K idle select 0:00 0.00% cron
14142 root 3 0 192K 480K idle ttyin 0:00 0.00% getty
28839 root 2 0 252K 444K idle select 0:00 0.00% inetd
1 root 10 0 352K 8K idle wait 0:00 0.00% init
23654 andrews 18 0 480K 8K idle pause 0:00 0.00% ksh
15315 root 2 0 240K 340K idle netio 0:00 0.00% syslogd
24014 andrews 2 0 1772K 392K idle netio 0:00 0.00% Xorg
27988 root -6 0 148K 428K idle htplev 0:00 0.00% hotplugd
11991 root 2 0 156K 452K idle kqread 0:00 0.00% apmd
9891 andrews 18 0 468K 8K idle pause 0:00 0.00% sh
5227 andrews 2 0 280K 320K idle select 0:00 0.00% ssh-agent
Test 1 summary
PID USERNAME PRI NICE SIZE RES STATE WAIT TIME CPU COMMAND
12371 andrews 2 0 5864K 5424K sleep select 0:20 4.05% Xorg
3123 andrews 2 0 1808K 6584K idle poll 0:05 0.00% xfwm4
8585 andrews 2 0 2280K 6476K sleep poll 0:06 0.00% xfdesktop
31620 andrews 2 0 5472K 11M sleep poll 0:41 9.33% xfce4-panel
32699 andrews 2 0 1852K 6948K idle poll 0:04 0.00% xftaskbar4
32600 andrews 2 0 856K 4424K idle poll 0:03 0.00% xfce4-session
26271 andrews 2 0 1500K 4724K sleep poll 0:02 0.00% xfce-mcs-mana
23208 andrews 2 0 8752K 15M sleep poll 0:24 5.27% AbiWord-2.4
Test 2 summary
PID USERNAME PRI NICE SIZE RES STATE WAIT TIME CPU COMMAND
2484 andrews 2 0 5632K 5180K run - 0:15 3.27% Xorg
31443 andrews 2 0 1756K 6472K idle poll 0:05 0.00% xfwm4
31105 andrews 2 0 2024K 5784K sleep poll 0:06 0.00% xfdesktop
3082 andrews 2 0 5240K 7792K run - 0:29 9.57% xfce4-panel
6667 andrews 2 0 1624K 6892K idle poll 0:05 0.00% xftaskbar4
5673 andrews 2 0 756K 4280K idle poll 0:03 0.00% xfce4-session
28783 andrews 2 0 1412K 4164K sleep poll 0:02 0.00% xfce-mcs-mana
31372 andrews 28 0 8604K 15M run - 0:23 4.30% AbiWord-2.4
Test 3 Summary
PID USERNAME PRI NICE SIZE RES STATE WAIT TIME CPU COMMAND
23689 andrews 2 0 5624K 5036K sleep select 0:17 8.25% Xorg
22566 andrews 2 0 1752K 6432K sleep poll 0:05 0.88% xfwm4
13100 andrews 2 0 2016K 5700K sleep poll 0:06 0.00% xfdesktop
15806 andrews 2 0 5244K 7628K run - 0:30 10.06% xfce4-panel
7526 andrews 2 0 1656K 6768K sleep poll 0:05 3.32% xftaskbar4
31169 andrews 2 0 764K 4196K sleep poll 0:03 0.00% xfce4-session
20358 andrews 2 0 1384K 4128K sleep poll 0:02 0.00% xfce-mcs-mana
2201 andrews 2 0 8604K 14M sleep poll 0:25 32.86% AbiWord-2.4
With such a rudimentary test we cannot begin to predict the real/page memory usage patterns, however, we can look at individual process memory utilisation based upon the SIZE and RES fields in the top display.
The RES field is the resident memory usage field for the process, whereas the size field is the total process size.
These fields may differ quite radically since the operating system may over-allocate memory to a process speculatively (accounting for a large RES field and a smaller SIZE field), an extremely large SIZE field and a small RES field may indicate that a significant amount of the process is paged out etc.
What we are looking for realistically in this test is a downward trend in these stats and almost without exception we see that trend in both size and resident statistics for each process.
Summary
It appears with these tunings we have freed some memory for use by other processes.
We should notice that in such an environment the systems will converge upon a good working set more rapidly and will therefore seem faster following initial boot and major memory reallocation.
We have also adopted an allocation flag that secures more frequent use of memory compaction techniques thus allowing more efficient use of the available memory.
