pagezero again

Suleiman Souhlal ssouhlal at
Fri May 12 17:51:38 PDT 2006

Ivan Voras wrote:
> Some time ago I reported that pagezero kernel thread sometime takes 
> (what seems to me) a too large chunk of available CPU (30%) on a very 
> busy web server. There were no replies :( Since then, I've reconfigured 
> apache to use PHP as a fastcgi module and the problem seems to have 
> gotten worse - now it *always* takes ~25-30% CPU, and my "System" time 
> stat shows it (its almost always ~30%).
>  From what I can understand, pagezero thread fills kernel's pool of 
> zeroed pages. This looks non-threteaning, but what would cause such high 
> demand of zeroed pages on my system? The number of processes is almost 
> constant, there are no frequent process spawnings or forks (top shows 
> "last pid" to be almost constant). FastCGI processes communicate over 
> UNIX sockets.
> Also, pagezero thread is (should be) executing at idle priority - does 
> this mean it won't interfere much with machine's performance? Even if 
> "0% idle" is not uncommon state?
> (This is FreeBSD 6.1-R, 2CPU SMP).

Can you give the output of top(1)? Until this is fixed, you can disable 
pagezero with sysctl vm.idlezero_enable=0.

-- Suleiman

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