Re: [RFC] Transparent on-demand memory setup initializationembedded in the (GFP) buddy allocator

[Nathan Zimmer]

On Wed, Jun 26, 2013 at 03:37:15PM +0200, Ingo Molnar wrote:
> 
> * Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> 
> > On Wed, 26 Jun 2013 11:22:48 +0200 Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> > 
> > > except that on 32 TB 
> > > systems we don't spend ~2 hours initializing 8,589,934,592 page heads.
> > 
> > That's about a million a second which is crazy slow - even my 
> > prehistoric desktop is 100x faster than that.
> > 
> > Where's all this time actually being spent?
> 
> See the earlier part of the thread - apparently it's spent initializing 
> the page heads - remote NUMA node misses from a single boot CPU, going 
> across a zillion cross-connects? I guess there's some other low hanging 
> fruits as well - so making this easier to profile would be nice. The 
> profile posted was not really usable.
> 
That is correct, from what I am seeing, using crude cycle counters, there is
far more time spent on the later nodes, i.e. memory near the boot node is 
initialized a lot faster then remote memory.

I think the other low hanging fruits are currently being drowned out by the
lack of locality.

Nate

> Btw., NUMA locality would be another advantage of on-demand 
> initialization: actual users of RAM tend to allocate node-local 
> (especially on large clusters), so any overhead will be naturally lower.
> 
> Thanks,
> 
> 	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/