Re: [RFC] [PATCH 8/9] memcg: remove page_cgroup pointer from memmap

[Balbir Singh]

KAMEZAWA Hiroyuki wrote:
> Remove page_cgroup pointer from struct page.
> 
> This patch removes page_cgroup pointer from struct page and make it be able
> to get from pfn. Then, relationship of them is
> 
> Before this:
>   pfn <-> struct page <-> struct page_cgroup.
> After this:
>   struct page <-> pfn -> struct page_cgroup -> struct page.
> 
> Benefit of this approach is we can remove 8(4) bytes from struct page.
> 
> Other changes are:
>   - lock/unlock_page_cgroup() uses its own bit on struct page_cgroup.
>   - all necessary page_cgroups are allocated at boot.
> 
> Characteristics:
>   - page cgroup is allocated as some amount of chunk.
>     This patch uses SECTION_SIZE as size of chunk if 64bit/SPARSEMEM is enabled.
>     If not, appropriate default number is selected.
>   - all page_cgroup struct is maintained by hash. 
>     I think we have 2 ways to handle sparse index in general
>     ...radix-tree and hash. This uses hash because radix-tree's layout is
>     affected by memory map's layout.
>   - page_cgroup.h/page_cgroup.c is added.
> 
> TODO:
>   - memory hotplug support. (not difficult)

Kamezawa,

I feel we can try the following approaches

1. Try per-node per-zone radix tree with dynamic allocation
2. Try the approach you have
3. Integrate with sparsemem (last resort for performance), Dave Hansen suggested
adding a mem_section member and using that.

I am going to try #1 today and see what the performance looks like


-- 
	Balbir
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