Re: [PATCH 16/22] Do not setup zonelist cache when there is only one node

David Rientjes
2009-04-22T20:34:46Z

On Wed, 22 Apr 2009, Lee Schermerhorn wrote:

> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index 7f45de1..e59bb80 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -1467,8 +1467,11 @@ this_zone_full:
> > > if (NUMA_BUILD)
> > > zlc_mark_zone_full(zonelist, z);
> >
> > If zonelist caching is never used for UMA machines, why should they ever
> > call zlc_mark_zone_full()? It will always dereference
> > zonelist->zlcache_ptr and immediately return without doing anything.
> >
> > Wouldn't it better to just add
> >
> > if (num_online_nodes() == 1)
> > continue;
> >
> > right before this call to zlc_mark_zone_full()? This should compile out
> > the remainder of the loop for !CONFIG_NUMA kernels anyway.
>
> Shouldn't it already do that? NUMA_BUILD is defined as 0 when
> !CONFIG_NUMA to avoid #ifdef's in the code while still allowing compiler
> error checking in the dead code.
>

Yeah, but adding the check on num_online_nodes() also prevents needlessly
calling zlc_mark_zone_full() on CONFIG_NUMA kernels when running on an UMA
machine.