04-08-2013
Quote:
Originally Posted by
butchie3980
the idea is to trigger swap usage, and we try to monitor that two ways, using top and "swap -l"
first step that we try is to fill up /tmp with a couple of simple "mkfile 10g /tmp/memeater01" style commands. We can see the available ram decrease each time we create one of those files in /tmp.
we get down to about 10-ish GB of free ram and start to encounter "no space available" errors when trying to create tmp files.
You have exhausted your virtual memory, which includes most of the RAM plus all of the swap area when you get these messages. Can you post the actual numbers and the commands you use to measure memory and swap usage ?
Quote:
Next think we tried was to push it over the edge using a program that simply uses malloc() calls to reserve ram and hold onto it. we can also watch the avalable ram decrease until the 10GB (roughly) threshold and then this program dies.
How (why) does it die ?
Quote:
A combination of both /tmp files and the malloc() program still dies around the 10gb free threshold and we never ever see any indicators that swap space is being used.
Are you you actually accessing all of the the allocated pages ?
Quote:
Just downloaded VTS, and started reading the documentation. Tried a test run, but don't know if the defaults are what we need. We only enabled the memory test and ran it. According to top, free RAM dropped to 36GB and stayed there, Free swap stayed the same no changes. We sat there and watched top for about 30 minutes before getting pulled away to a meeting. so we stopped it and decided to try later. are there some parameters we need to set or change?
VTS is to stress test you hardware in order to detect faulty components. I don't think this is what you are looking for, although I don't precisely understand what exactly you are trying to achieve/fix ...
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RAM(4) Kernel Interfaces Manual RAM(4)
NAME
ram - ram disk driver
SYNOPSIS
/sys/conf/SYSTEM:
NRAM ram_size # RAM disk size (512-byte blocks)
major device number(s):
block: 3
minor device encoding:
must be zero (0)
DESCRIPTION
The ram pseudo-device provides a very fast extended memory store. It's use is intended for file systems like /tmp and applications which
need to access a reasonably large amount of data quickly.
The amount of memory dedicated to the ram device is controlled by the NRAM definition in units of 512-byte blocks. This is also patchable
in the system binary through the variable ram_size (though a patched system would have to be rebooted before any change took effect; see
adb(1)). This makes it easy to test the effects of different ram disk sizes on system performance. It's important to note that any space
given to the ram device is permanently allocated at system boot time. Dedicating too much memory can adversely affect system performance
by forcing the system to swap heavily as in a memory poor environment.
The block file accesses the ram disk via the system's buffering mechanism through a buffer sharing arrangement with the buffer cache. It
may be read and written without regard to physical disk records. There is no `raw' interface since no speed advantage is gained by such an
interface with the ram disk.
DISK SUPPORT
The ram driver does not support pseudo-disks (partitions). The special files refer to the entire `drive' as a single sequentially
addressed file.
A typical use for the ram disk would be to mount /tmp on it. Note that if this arrangement is recorded in /etc/fstab then /etc/rc will
have to be modified slightly to do a mkfs(8) on the ram disk before the standard file system checks are done.
FILES
/dev/ram block file
/dev/MAKEDEV script to create special files
/dev/MAKEDEV.local script to localize special files
SEE ALSO
hk(4), ra(4), rl(4), rk(4), rp(4), rx(4), si(4), xp(4) dtab(5), autoconfig(8)
DIAGNOSTICS
ram: no space. There is not enough memory to allocate the space needed by the ram disk. The ram disk is disabled. Any attempts to access
it will return an error.
ram: not allocated. No memory was allocated to the ram disk and an attempt was made to open it. Either not enough memory was available at
boot time or the kernel variable ram_size was set to zero.
BUGS
The ram driver is only available under 2.11BSD.
3rd Berkeley Distribution Januray 27, 1996 RAM(4)