[LON-CAPA-admin] memory and httpd processes

[Jim Maxka]

Hi Martin -- thanks for clearing this up for me.  Tonight is a light 
load.  I believe I have noticed differences in swap space used under 
very heavy load.  But I need some proof.  So, I will try to replicate 
this situation and report back.  --jim
Martin Siegert wrote:

>On Wed, May 04, 2005 at 10:01:00PM -0600, Todd Ruskell wrote:
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>>Jim,
>>
>>This doesn't surprise me too much.  One thing about top is that the reported 
>>amount of memory used includes all kinds of cached data that isn't really 
>>"used" in the sense that it contains crucial code for a currently running 
>>process.  It is only "used" in the sense that it contains a bunch of data 
>>that was accessed recently, and some process decided it might improve 
>>response times if this data were kept in memory rather than always going out 
>>to disk, for example.  I haven't checked my servers regularly, but on my 
>>desktop machines, top nearly always reports I am at full memory use, even 
>>though I know the currently loaded programs aren't that big.  My guess is 
>>that when you stop httpd, it intelligently tells the kernel to *really* let 
>>that memory go.
>>    
>>
>
>I must agree with your assessment: The Linux kernel regards "free" memory
>as wasted memory, thus it uses memory for all kinds of purposes. In fact,
>I would expect that top almost always shows almost all of the memory in use.
>This does not mean much.
>The one parameter that I found somewhat reliable in top's output is the
>amount of swap space used. As long as that remains small everything is
>fine. Since that number actually remained the same in the example I
>would say that nothing much changed due to the restart.
>
>  
>
>>As to why this drastically improves performance, I will let those with much 
>>more knowledge answer that question more intelligently than I can.
>>    
>>
>
>Does it really improve performance or is that more an illusion?
>
>Cheers,
>Martin
>
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