Re: [gentoo-user] mysqld invoked oom-killer

[Dale]

Grant wrote:
> ...
>
>> To confuse you even more, there is a swappiness setting as well.  On my old
>> x86 rig, I have 2Gbs of ram.  My hard drive is really slow since it is IDE.
>>   I set swappiness to 20.  That tells the kernel that I have swap space but
>> don't use it unless you must.  For what I use the rig for, 2Gbs is plenty of
>> ram.  The lower the swappiness setting, the less the kernel will try to use
>> ram.  The higher the setting, the more it will try to use swap.
>>
>> I have a new rig that is amd64 and has SATA drives which are pretty fast.  I
>> still have swappiness set to 20.  Why do I have it set to 20 when the drives
>> are faster you ask?  I have it set to 20 because I have 16Gbs of ram here.
>>   Even if I have portage's work directory on tmpfs and am compiling OOo, it
>> should not need swap then either.
>>
>> By the way, my swap partition is 1Gb on both systems.  Why have it this way
>> since one machine has 2Gbs and one has 16Gbs?  As it has been said, you want
>> a little swap and even using a little swap is OK.  You just don't want it to
>> be using swap and actually swapping data all the time.  On my old rig, it
>> started out with 512Mbs.  I use KDE and it got to the point where it was
>> using enough ram that it was not just using swap and letting things sit, it
>> was actively swapping data from swap and doing so a lot.  It would only be
>> using a 100Mbs sometimes 200Mbs.  The point is, it was slowing the system
>> down because of the swapping process.  I bought a stick of ram and all was
>> well again.  It would still use a 100Mbs of swap at times but it would not
>> be actively swapping the data back and forth so it wasn't a big deal.
>>
>> I think the point is this, it is good to have a little swap.  It is even OK
>> for it to use a little swap when it is mostly sitting there.  When you
>> notice it using swap and it is actively swapping and moving things back and
>> forth, you need more memory.  Having the swap may can save you from a crash
>> but is can also give you a "time to add more ram" hint too.  If Linux starts
>> using swap a good bit, you need more ram.
>>
> OK, how can you determine when a machine is actively swapping and
> moving things back and forth?  Do you need to monitor the system with
> a real-time tool during peak usage?
>
> - Grant
>
>
>

I use gkrellm on mine.  It has a little charty thingy.  I think iotop 
will show if anything is being swapped to.  There may be others as well 
for a console or non-X machine.  Most people know of top but that really 
doesn't help a lot.  It doesn't show things moving just how much is 
being used.  I think there is a better command that shows this but dang 
if I can recall it right now.  Somebody help a old fart out here.  lol

Dale

:-)  :-)