On Fri, Jul 17, 2015 at 02:17:29PM +0100, Mel Gorman wrote:
> On Fri, Jul 17, 2015 at 03:12:32PM +0200, Peter Zijlstra wrote:
> > On Fri, Jul 17, 2015 at 01:22:04PM +0100, Mel Gorman wrote:
> > > int __meminit early_pfn_to_nid(unsigned long pfn)
> > > {
> > > + static DEFINE_SPINLOCK(early_pfn_lock);
> > > int nid;
> > >
> > > - /* The system will behave unpredictably otherwise */
> > > - BUG_ON(system_state != SYSTEM_BOOTING);
> > > + /* Avoid locking overhead during boot but hotplug must lock */
> > > + if (system_state != SYSTEM_BOOTING)
> > > + spin_lock(&early_pfn_lock);
> > >
> > > nid = __early_pfn_to_nid(pfn, &early_pfnnid_cache);
> > > - if (nid >= 0)
> > > - return nid;
> > > - /* just returns 0 */
> > > - return 0;
> > > + if (nid < 0)
> > > + nid = 0;
> > > +
> > > + if (system_state != SYSTEM_BOOTING)
> > > + spin_unlock(&early_pfn_lock);
> > > +
> > > + return nid;
> > > }
> >
> > Why the conditional locking?
>
> Unnecessary during boot when it's inherently serialised. The point of
> the deferred initialisation was to boot as quickly as possible.
Sure, but does it make a measurable difference?
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