On Wed, 17 Sep 2008 16:28:26 -0700 Balbir Singh  wrote:
>

quoted text
> Before trying the sparsemem approach, I tried a radix tree per node,

> per zone and I seemed to actually get some performance

> improvement.(1.5% (noise maybe))

>

> But please do see and review (tested on my x86_64 box with unixbench

> and some other simple tests)

>

> v4..v3

> 1. Use a radix tree per node, per zone

>

> v3...v2

> 1. Convert flags to unsigned long

> 2. Move page_cgroup->lock to a bit spin lock in flags

>

> v2...v1

>

> 1. Fix a small bug, don't call radix_tree_preload_end(), if preload fails

>

> This is a rewrite of a patch I had written long back to remove struct page

> (I shared the patches with Kamezawa, but never posted them anywhere else).

> I spent the weekend, cleaning them up for 2.6.27-rc5-mmotm (29 Aug 2008).

>

> I've tested the patches on an x86_64 box, I've run a simple test running

> under the memory control group and the same test running concurrently under

> two different groups (and creating pressure within their groups).

>

> 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? ;)
(IOW, your changelog is in the category "sucky", along with 90% of the others)

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