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

[Paul Jackson <pj@sgi.com>]

David wrote:
> The only change that would be required is 
> to abstract a macro to test against if NUMA emulation was configured 
> correctly at boot-time instead of just NUMA_BUILD.

Why add any logic to avoid this zonelist caching on systems not using
numa emulation?

Leaving this zonelist caching enabled all the time:
 1) improves test coverage of it, and
 2) benefits those real numa systems that might have
    long zonelist scans in the future.

My experience on my current customer base with cpusets is almost
entirely with HPC (High Performance Computing) apps, which usually
manage their memory layout very closely.  These workloads would tend to
have very short zonelist scans and benefit little from this speed up.

As cpusets gets wider use on more varied workloads, I would expect
that some of these varied workloads would stress the zonelist scanning
more.

And there's still a pretty good chance, though I can't document it,
that we've already seen performance problems, even on existing HPC
workloads, with this zonelist scan.

So ... I ask again ... why avoid this speed up on systems not emulating
nodes?

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

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>