Re: Note describing poor dcache utilization under high memory pressure

[Daniel Phillips]

On January 29, 2002 10:20 am, Momchil Velikov wrote:
> >>>>> "Daniel" == Daniel Phillips <[e-mail]> writes:
> 
> Daniel> On January 29, 2002 09:39 am, Momchil Velikov wrote:
> >> >>>>> "Oliver" == Oliver Xymoron <[e-mail]> writes:
> Oliver> you can't actually _share_ the page tables without marking the pages
> Oliver> themselves readonly.
> >> 
> >> Of course, ptes are made COW, just like now. Which brings up the
> >> question how much speedup we'll gain with a code that touches every
> >> single pte anyway ?
> 
> Daniel> It's only touching the ptes on tables that are actually used, so if a parent
> Daniel> with a massive amount of mapped memory forks a child that only instantiates
> Daniel> a small portion of it (common situation) then the saving is pretty big.
> 
> Umm, all the ptes af the parent ought to be made COW, no ?

My explanation above is borked, please see my reply to wli.  In short, each 
page table of the parent is already either shared - in which case the CoW 
ptes are already marked RO - or it was instantiated by the parent, in which 
case the work of marking its pte's RO is insignificant, and is certainly not 
more than the cost incurred by the current method.

-- 
Daniel