Re: 2.6.9-rc1: page_referenced_one() CPU consumption
From: Nick Piggin
Date: Sun Sep 12 2004 - 23:56:56 EST
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!
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