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From Ian Holsman <i...@apache.org>
Subject Re: performance: using mlock(2) on httpd parent process
Date Wed, 20 Mar 2002 19:19:44 GMT
Aaron Bannert wrote:
> On Thu, Mar 21, 2002 at 02:14:04AM +0800, Stas Bekman wrote:
> 
>>But if the system needs to page things out, most of the parent process's 
>> pages will be scheduled to go first, no? So we are talking about a 
>>constant page-in/page-out from/to the parent process as a performance 
>>degradation rather than memory unsharing. Am I correct?
> 
> [...]
> 
>>Well, the system coming close to zero of real memory available. The 
>>parent process starts swapping like crazy because most of its pages are 
>>LRU, slowing the whole system down and if the load doesn't go away, the 
>>system takes a whirl down to a halt.
> 
> 
> FWIW, Solaris 8 introduced "priority paging", which basicly means
> that pages that are non-executable will be swapped out earlier than
> higher-priority executable pages. This of course introduces nasty little
> tricks like marking a data file as executable just to ensure that it
> gets priority paging.

priority paging is more to do with the filesystem cache than anything 
else. in low memory conditions it start freeing pages used by the file 
cache first. without it you could swap your machine to death by copying
a 1 gig file around the place.


> 
> I'm not sure how this affects mod_perl and it's "data is runtime-compiled
> bytecode" situation, but it means that we get it for free w/ httpd and
> all its dependent libraries (and DSOs).
> 
> -aaron
> 
> p.s. It can be enabled on Solaris 7, it's just not on by default.
> 




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