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

From: Balbir Singh
Date: Tue Sep 09 2008 - 00:34:53 EST

KAMEZAWA Hiroyuki wrote:
> On Mon, 8 Sep 2008 20:58:10 +0530
> Balbir Singh <balbir@xxxxxxxxxxxxxxxxxx> wrote:
>> Sorry for the delay in sending out the new patch, I am traveling and
>> thus a little less responsive. Here is the update patch
> Hmm.. I've considered this approach for a while and my answer is that
> this is not what you really want.
> Because you just moves the placement of pointer from memmap to
> radix_tree both in GFP_KERNEL, total kernel memory usage is not changed.

Agreed, but we do reduce the sizeof(struct page) without adding on to
page_cgroup's size. So why don't we want this?

> So, at least, you have to add some address calculation (as I did in March)
> to getting address of page_cgroup.

What address calculation do we need, sorry I don't recollect it.

But page_cgroup itself consumes 32bytes
> per page. Then.....
> My proposal to 32bit system is following
> - remove page_cgroup completely.
> - As a result, there is no per-cgroup lru. But it will not be bad
> bacause the number of cgroups and pages are not big.
> just a trade-off between kernel-memory-space v.s. speed.

32 bit systems with PAE can support quite a lot of memory, so I am not sure I
agree. I don't like this approach

> - Removing page_cgroup and just remember address of mem_cgroup per page.

This is on top of the suggested approach above?

> How do you think ?

I don't like the approach.

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