Re: [RFC][PATCH] Clarify mem_cgroup lock handling and avoid races.

[Balbir Singh <balbir@linux.vnet.ibm.com>]

KAMEZAWA Hiroyuki wrote:
> On Thu, 21 Feb 2008 18:07:45 +0900 (JST)
> Hirokazu Takahashi <taka@valinux.co.jp> wrote:
>>> But we'll be able to archive  pfn <-> page_cgroup relationship using
>>> on-demand memmap style.
>>> (Someone mentioned about using radix-tree in other thread.)
>> My concern is this approach seems to require some spinlocks to protect the
>> radix-tree. 
> 
> Unlike file-cache, radix-tree enries are not frequently changed.
> Then we have a chance to cache recently used value to per_cpu area for avoiding
> radix_tree lock.
> 
> But yes. I'm afraid of lock contention very much. I'll find another lock-less way
> if necessary. One idea is map each area like sparsemem_vmemmap for 64bit systems.
> Now, I'm convinced that it will be complicated ;)
> 

The radix tree base is lockless (it uses RCU), so we might have a partial
solution to the locking problem. But it's unchartered territory, so no one knows.

> I'd like to start from easy way and see performance.
> 

Sure, please keep me in the loop as well.

> Thanks,
> -Kame


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL

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