Re: [PATCH] page allocator: fix update NR_FREE_PAGES only as necessary

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index 4e4b5b3..87976ad 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -1244,6 +1244,9 @@ again:
> > >         return page;
> > >  
> > >  failed:
> > > +       spin_lock(&zone->lock);
> > > +       __mod_zone_page_state(zone, NR_FREE_PAGES, 1 << order);
> > > +       spin_unlock(&zone->lock);
> > >         local_irq_restore(flags);
> > >         put_cpu();
> > >         return NULL;
> > 
> > Why can't we write following? __mod_zone_page_state() only require irq
> > disabling, it doesn't need spin lock. I think.
> > 
> 
> Adding Christoph to be sure but yes, as this is a per-cpu variable it
> should be safe to update with __mod_zone_page_state() as long as
> interrupts and preempt are disabled. If true, then this is a neater fix
> and is also needed for -stable 2.6.31 and 2.6.32.
> 
> Well spotted and thanks.

Yes, it should be sent to -stable tree. I hope this fix also solve recent mysterious
allocation failure problem ;-)



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