Re: 2.6.9-rc1: page_referenced_one() CPU consumption

[Nick Piggin <nickpiggin@yahoo.com.au>]

Nikita Danilov wrote:

> I ran tests few times, and difference between patched and un-patched
> kernels is within noise, so you are right, try-lock does not help.
> 

Well I'm glad - because I much prefer the spin_lock over the trylock :)

> But now I have new great idea instead. :)
> 
> I think page_referenced() should transfer dirtiness to the struct page
> as it scans pte's. Basically the earlier we mark page dirty the better
> file system write-back performs, because page has more chances to be
> bulk-written by ->writepages(). This is better than my previous patches
> to this end (that used separate function to transfer dirtiness from
> pte's to the page), because
> 
>     - locking overhead is avoided
> 
>     - it's simpler.
> 
> Nick, are you still in business of benchmarking random VM patches? :-)
> 

Yeah I am, and I do have that patch sitting around. It can *really*
help for writeout via maped memory (obviously doesn't help write()).

I think Andrew's response was that it can theoretically cause writeout
for workloads that don't want it, so I should come up with at least
one real-world improvement!