Re: [RFC 1/3] Framework for accurate node based statistics

[Nick Piggin <nickpiggin@yahoo.com.au>]

Christoph Lameter wrote:
> On Thu, 8 Dec 2005, Nick Piggin wrote:
> 
> 
>>Christoph Lameter wrote:
>>
>>>On Wed, 7 Dec 2005, Nick Piggin wrote:
>>>
>>>>Sorry, I think I meant: why don't you just use the "add all counters
>>>>from all per-cpu of the node" in order to find the node-statistic?
>>>
>>>which function is that?
>>>
>>
>>I'm thinking of get_page_state_node... but that's not quite the same
>>thing. I guess sum all per-CPU counters from all zones in the node,
>>but that's going to be costly on big machines.
> 
> 
> The per cpu counters count when a cpu did an allocation. They do not count 
> on which node the allocation was done and are thereofre not useful to 
> determine the memory use on one node.
> 

Yes, not that exact function of course.

> 
>>So I'm not sure, I guess I don't have any bright ideas... there is the
>>batching approach used by current pagecache_acct - is something like
>>that not sufficient either?
> 
> 
> The framework provides a similar approach by keeping differential 
> counters for each processor.
> 

But the accounting delay has the unbounded error problem that the
batching approach does not.

-- 
SUSE Labs, Novell Inc.

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