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.
--
Mel Gorman
SUSE Labs
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