Re: The hall of bloat

[Soeren Sandmann <sandmann daimi au dk>]

Alan Cox <alan lxorguk ukuu org uk> writes:

> On Llu, 2005-05-16 at 06:45, Mark McLoughlin wrote:
> > On Sun, 2005-05-15 at 13:57 -0500, William Lovaton wrote:
> > 
> > > Reading your little chat with the kernel guys it seems that there is
> > > little benefit (or none) in reducing VM Size, why is that?
> > 
> > 	Because the kernel won't back this mapping with physical memory until
> > the application actually tries to use it - i.e. only when the app tries
> > to write to any these pages does the kernel get a page fault and
> 
> There is a cost if the mapping has just a few random pages filled as you
> have to fill in the whole page table heirarchy down to the page in
> question. 

Isn't it always the case that you have to fill in the page table
hierarchy down to the pages that you are actually using, regardless of
the size of the mapping? Why would a mapping of 8K with both pages
used require more page table entries than a mapping of 10M with two
pages used?


Søren