Re: [PATCH 10/13] x86: mm: Enable deferred struct page initialisation on x86-64

[Waiman Long]

On 04/23/2015 05:23 AM, Mel Gorman wrote:
> On Wed, Apr 22, 2015 at 04:45:00PM -0700, Andrew Morton wrote:
> > On Wed, 22 Apr 2015 18:07:50 +0100 Mel Gorman<mgorman@xxxxxxx>  wrote:
> >
> > > --- a/arch/x86/Kconfig
> > > +++ b/arch/x86/Kconfig
> > > @@ -32,6 +32,7 @@ config X86
> > >   	select HAVE_UNSTABLE_SCHED_CLOCK
> > >   	select ARCH_SUPPORTS_NUMA_BALANCING if X86_64
> > >   	select ARCH_SUPPORTS_INT128 if X86_64
> > > +	select ARCH_SUPPORTS_DEFERRED_STRUCT_PAGE_INIT if X86_64&&  NUMA
> > Put this in the "config X86_64" section and skip the "X86_64&&"?
> Done.
>
> > Can we omit the whole defer_meminit= thing and permanently enable the
> > feature?  That's simpler, provides better test coverage and is, we
> > hope, faster.
> Yes. The intent was to have a workaround if there were any failures like
> Waiman's vmalloc failures in an earlier version but they are bugs that
> should be fixed.
>
> > And can this be used on non-NUMA?  Presumably that won't speed things
> > up any if we're bandwidth limited but again it's simpler and provides
> > better coverage.
> Nothing prevents it. There is less opportunity for parallelism but
> improving coverage is desirable.

Memory access latency can be more than double for local vs. remote node 
memory. Bandwidth can also be much lower depending on what kind of 
interconnect is between the 2 nodes. So it is better to do it in a 
NUMA-aware way. Within a NUMA node, however, we can split the memory 
initialization to 2 or more local CPUs if the memory size is big enough.

Cheers,
Longman
--
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/