RFE: Increase NR_CPUS to 4096

[Prarit Bhargava]

On 07/15/2013 04:14 PM, Josh Boyer wrote:
> On Mon, Jul 15, 2013 at 1:21 PM, Prarit Bhargava <prarit at redhat.com> wrote:
>> I've done some testing across various systems (both "large" and "small").
>> Increasing NR_CPUS seems to have a negligible effect.  I see about a 1.1M
>> increase in memory usage when switching between 128 cpus and 5120 cpus.  Since
>> most systems ship with 4G or more these days, I cannot see an issue with
>> consuming a small amount of memory like this.
> 
> 1.1M isn't small.  We recently declined to build btrfs into the kernel
> because it increased the overall memory usage by a similar amount.
> Also, we regularly see users and bug reports still in the 2G range.

OOC what was the objection to 1M?  Is there some lower limit I should be
concerned about?

> While it's not an apples to apples comparison, far more Fedora users
> are going to be using btrfs than > 128 CPUs.  I'm not saying no
> immediately, but I'm kinda dubious as to the benefits for Fedora.
> 

We're already exceeding 128 cpus on a regular basis (or at least I am).  Getting
testing in the upper range only improves Fedora ... IMO.

P.

> josh