Re: uarea swap-out

[yamt%mwd.biglobe.ne.jp@localhost (YAMAMOTO Takashi)]

hi,

> matthew green <mrg%eterna.com.au@localhost> wrote:
>> 
>> i'm really curious how this affects platforms with very
>> few hardware pages, like acorn26.

saving some pages is one thing, but i think the more important point of
swapping is thrashing control.  ie. by suspending processes in turn,
you might be able to run others with less vm pressure.

>> 
> 
> I cannot measure that empirically, therefore CC'ing port-acorn26 and
> port-acorn32 lists. There are few points regarding this:
> 
> - Merge of lwp_cache and uarea (it puts struct lwp, pcb and kstack together)
>   should have positive effect i.e. it would increase the utilisation of pages.
> 
> - The criteria when LWP can be swapped-out is relatively strict i.e. there
>   are already many states when it cannot, see swappable() in uvm_glue.c.
> 
> - If your machine starts swapping uareas, I think it is already quite a
>   hammer, especially for machines like acorn26/32.
> 
> Newer patch removing uarea swap-out:
> 
> http://www.netbsd.org/~rmind/uarea_swapout3.diff

calling uvm_fault_wire on wired pages seems wrong.

YAMAMOTO Takashi

> 
> By the way, patch cuts ~4k from amd64 kernel size.
> 
>> 
>> .mrg.
> 
> -- 
> Mindaugas