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

Hi,

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.

I think this design is just temporary and the goal is to pre-allocate
all page_cgroups at boot time if it isn't disabled.

But I think each memory model type should have its own way of managing
its page_cgroup arrays as doing for its struct page arrays.
It would be better rather than the sparsemem approach he said.

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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