Re: PG_zero

[Andrea Arcangeli <andrea@novell.com>]

On Tue, Nov 02, 2004 at 01:53:09PM +0000, Andy Whitcroft wrote:
> I'll have a look out for the results, they should be around somewhere?

could you give an hint on which workload to use for the measurements?

> page for use.  The colder the page the slower the system went.

this is expected. This is why I waste no more than 4k of cache for each
local-apic irq, and this is also why I don't waste any cache at all if
the zerolist is already full or the hot-cold list is empty (plus if
there are PG_zero pages in the hot-cold list since I cache PG_zere deep
down in the buddy, I don't waste any cache at all by refiling them into
the zero quicklist). Not sure if you were using the same design. Note
that idle zeroing is a worthless feature in my patch, I never intented
to implement it, I just happened to be able to implement it with a
trivial change so I did (and it can be disabled via sysctl). all the
important stuff are bugfixes and obsoleting the inefficient slab for pte
allocation and to create a superset of the pte_quicklist in 2.4 that is
missing in 2.6 by mistake.

Note that I'm keeping track of hot and cold cache for the zerolist too.
Plus I can disable the idle zeroing and still I will be able to cache
zero information in O(1) (so then caching zero will be zerocost, plus
I'll keep track of the hottest zero page, and the coldest one).