Re: [RFC][PATCH] Remove cgroup member from struct page (v3)

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

On Wed, 17 Sep 2008 18:40:08 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:
> > Advantages of the patch
> > 
> > 1. It removes the extra pointer in struct page
> > 
> > Disadvantages
> > 
> > 1. Radix tree lookup is not an O(1) operation, once the page is known
> >    getting to the page_cgroup (pc) is a little more expensive now.
> 
> Why are we doing this?  I can guess, but I'd rather not have to.
> 
> a) It's slower.
> 
> b) It uses even more memory worst-case.
> 
> c) It uses less memory best-case.
> 
> someone somewhere decided that (Aa + Bb) / Cc < 1.0.  What are the values
> of A, B and C and where did they come from? ;)
> 

Balbir, don't you like pre-allocate-page-cgroup-at-boot at all ?
I don't like radix-tree for objects which can spread to very vast/sparse area ;)

BTW, I already have lazy-lru-by-pagevec protocol on my patch(hash version) and
seems to work well. I'm now testing it and will post today if I'm enough lucky.

Thanks,
-Kame

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