[rhelv6-beta-list] My first experiences with RHEL6 beta

[James Findley]

On 06/15/2010 03:00 AM, John Summerfield wrote:
> Jonathan Billings wrote:
>> On Tue, Jun 15, 2010 at 08:22:27AM +0800, John Summerfield wrote:
>>> Jonathan S Billings wrote:
>>>> Swap improves performance on a system, due to the way the Linux memory
>>>> manager works. Swap partitions are faster than swap files, and less
>>>> likely to be lost, corrupted or removed by accident.
>>> The performance claim has not been true for some time, I think as far
>>> back as 2.4.
>>
>> The performance of a swap file vs. a swap partition is similar, I
>> admit I was unaware of that. However, the performance of the linux
>> memory manager IS improved by having available swap.
>
> in these cases?
> 09:22 [summer at penguin tmp]$ swapon -s
> 09:47 [summer at penguin tmp]$ ssh ns swapon -s
> bash: swapon: command not found
> 09:47 [summer at penguin tmp]$ root ns swapon -s
> Filename Type Size Used Priority
> /var/swapfile file 524280 1448 -1
> Connection to ns closed.
> 09:47 [summer at penguin tmp]$ root 192.168.4.253 swapon -s
> Connection to 192.168.4.253 closed.
> 09:47 [summer at penguin tmp]$ root mail.office.lan swapon -s
> function siteBlock { echo $1 | tee -a /etc/squid/block.txt; }
> function siteKill { echo $1 | tee -a /etc/squid/kill; }
> Filename Type Size Used Priority
> /var/swapfile file 524280 6140 4
> /var/swapfile1 file 1048568 0 1
> Connection to mail.office.lan closed.
> 09:48 [summer at penguin tmp]$

Oh no! rsync doesn't really care if you have a swap file or not in your 
arbitrary, naive test.  That doesn't mean anything.
Certain dirty memory structures can be more effectively flushed if they 
can be swapped out first.  This will use a few KB of swap, and only 
generate a negligible amount of disk IO.


>
> Penguin is my desktop, it has 8 Gbytes of RAM.
> ns is my office server, for the moment is got a Celeron, I think. It's a
> stand-in for a recently-deceased Athlon-XP system with 512-1Gbyte RAM.
> x.x.x.253 is my server/internet gateway. It has 5 Gbytes RAM.
> mail.office.lan is another internet gateway/server I manage. it's
> Pentium IV, has 512 Mbytes of RAM. It has that much swap because we used
> to run an rsync job that used it. rsync is the only program I've seen
> that can use extravagant amounts of virtual memory and not cause thrashing.
>
> I don't see that any of these systems (I have some more!) would benefit
> from having a swap partition.
>
> My virtual machine is a good approximation of what I expect to use into
> the next few years.
>
>
>
>>
>>> RAM for a typical SOHO system costs less than the time to acquire it
>>> and install it. The difference in cost is simply not relevant.
>>
>> When I spoke of memory being expensive compared to disk, I was
>> speaking of how resources are limited on a system hosting one or more
>> virtual machines. It's easy to host several fully populated virtual
>> machines on commodity hardware, however, it's more difficult to run
>> several virtual machines using the typical amount of memory. I should
>> have made that more clear.
>
> I will only speak to _my_ usage. Some of the assumptions behind RHEL
> seem to be a poor fit for environments I work in.
>
>

Nevermind, another distro might fit you better.  No operating system is 
meant to be perfect for everyone on the planet.