Re: [PATCH 00/14] Zoned VM counters V5

[Christoph Lameter <clameter@sgi.com>]

On Wed, 21 Jun 2006, Martin Bligh wrote:

> > So we now do two atomic ops for every 32 increments (threshold). If we
> > increment the threshhold then we reduce the atomic overhead but this also
> > influences the inaccurary of the global and per zone counter because there
> > is the potential of more counter update deferrals. Keeping the threshold low
> > makes the global and per zone counter more up to date.
> > I think 32 is a good compromise.
> 
> Ah, makes sense ... so the intent is get an an approximation. If you
> want accurate numbers, you still need to walk the per-cpu counters ...
> is that too slow for where you're reading it? didn't seem like a
> fastpath to me, given that balance_dirty_pages was already ratelimited?
> I guess it's still better than what we're doing now though ;-)

No you never walk per cpu counters. The advantage here is that the 
counters are always available without walking. Counters are regularly 
folded into the per zone and global counters via the cache reaper. 

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