superpages and kmem on amd64

User Wojtek wojtek at
Sun May 20 20:22:23 UTC 2012

>>> vm.pmap.pde.demotions: 31
>> No, your conclusion is incorrect.  These counts show that 543 superpage
>> mappings were created by promotion.
> OK, that sounds promising.  Does "created by promotion" count reflect
> historic / cumulative stats, or is vm.pmap.pde.promotions the actual number
> of superpages active?  Or should we subtract vm.pmap.pde.demotions from it to
> get the current value?

correction to my last answer. something is just wrong IMHO
on my 2GB laptop:

[root at wojtek ~]# sysctl -ad vm.pmap.pde
vm.pmap.pde: 2MB page mapping counters
vm.pmap.pde.promotions: 2MB page promotions
vm.pmap.pde.p_failures: 2MB page promotion failures
vm.pmap.pde.mappings: 2MB page mappings
vm.pmap.pde.demotions: 2MB page demotions
[root at wojtek ~]# sysctl -a vm.pmap.pde
vm.pmap.pde.promotions: 61196
vm.pmap.pde.p_failures: 4796
vm.pmap.pde.mappings: 3051
vm.pmap.pde.demotions: 2306

from description seems like mappings could be current amount , but both 
it's value as well as promotions-demotions gives nonsense.

with 2GB RAM there can not be 3051 or more 2MB pages mapped!

and i - at present - doesn't run many large programs actually only some 
xterms and one compiling task.

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