Re: follow_page()

Arjan van de Ven
2004-11-11T10:56:10Z

On Thu, 2004-11-11 at 02:40 -0800, Andrew Morton wrote:
> Can anyone think of a sane reason why this thing is marking the page dirty?
>
> I mean, we're supposed to mark the page dirty _after_ modifying its
> contents.

most likely it's because the intent to write to it is given.
It's cheaper for the OS to mark a pagetable dirty than it's for the CPU
to do so (example, on a Pentium 4 it can easily take the cpu 2000 to
4000 cycles to flip the dirty bit on the PTE). So if you KNOW you're
going to write to it (and thus the intent parameter) you can save a big
chunk of those cycles.