Re: [RFC] another way to speed up fake numa node page_alloc

[Paul Jackson <pj@sgi.com>]

David wrote:
> I'm talking about this:
> 
> +struct zonelist_faster {
> +	nodemask_t fullnodes;		/* nodes recently lacking free memory */
> +	unsigned long last_full_zap;	/* jiffies when fullnodes last zero'd */
> +	unsigned short node_id[MAX_NUMNODES * MAX_NR_ZONES]; /* zone -> nid */
> +};
> 
> With NODES_SHIFT equal to 10 as you recommend, you can't get away with an 
> unsigned short there. 


Apparently it's time for me to be a stupid git again.  That's ok; I'm
getting quite accustomed to it.

Could you spell out exactly why I can't get away with an unsigned short
node_id if NODES_SHIFT is 10?

I was thinking that limiting node_id to an unsigned short just meant
that we couldn't have more than 65536 nodes on the system.  That should
be enough, for a while anyway.

Indeed, given this line in include/linux/mempolicy.h:

	short            preferred_node;

I didn't even think I was being very original in this.


> Likewise, your nodemask_t would need to be 128 bytes.

Yes - big honkin NUMA iron calls for big nodemasks.  That's part of
why I spent the better part of a year driving Andrew to drink with
my cpumask/nodemask patches from hell.

Is there a problem with a 128 byte nodemask_t that I'm missing?

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@sgi.com> 1.925.600.0401

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