Re: [PATCH 3/3] memory_hotplug: Don't modify the zone_start_pfn outsideof zone_span_writelock()

[Ni zhan Chen]

On 09/28/2012 03:29 PM, Lai Jiangshan wrote:
> Hi, Chen,
>
> On 09/27/2012 09:19 PM, Ni zhan Chen wrote:
> > On 09/27/2012 02:47 PM, Lai Jiangshan wrote:
> > > The __add_zone() maybe call sleep-able init_currently_empty_zone()
> > > to init wait_table,
> > >
> > > But this function also modifies the zone_start_pfn without any lock.
> > > It is bugy.
> > >
> > > So we move this modification out, and we ensure the modification
> > > of zone_start_pfn is only done with zone_span_writelock() held or in booting.
> > >
> > > Since zone_start_pfn is not modified by init_currently_empty_zone()
> > > grow_zone_span() needs to check zone_start_pfn before update it.
> > >
> > > CC: Mel Gorman <mel@xxxxxxxxx>
> > > Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
> > > Reported-by: Yasuaki ISIMATU <isimatu.yasuaki@xxxxxxxxxxxxxx>
> > > Tested-by: Wen Congyang <wency@xxxxxxxxxxxxxx>
> > > ---
> > >    mm/memory_hotplug.c |    2 +-
> > >    mm/page_alloc.c     |    3 +--
> > >    2 files changed, 2 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > > index b62d429b..790561f 100644
> > > --- a/mm/memory_hotplug.c
> > > +++ b/mm/memory_hotplug.c
> > > @@ -205,7 +205,7 @@ static void grow_zone_span(struct zone *zone, unsigned long start_pfn,
> > >        zone_span_writelock(zone);
> > >          old_zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
> > > -    if (start_pfn < zone->zone_start_pfn)
> > > +    if (!zone->zone_start_pfn || start_pfn < zone->zone_start_pfn)
> > >            zone->zone_start_pfn = start_pfn;
> > >          zone->spanned_pages = max(old_zone_end_pfn, end_pfn) -
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index c13ea75..2545013 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -3997,8 +3997,6 @@ int __meminit init_currently_empty_zone(struct zone *zone,
> > >            return ret;
> > >        pgdat->nr_zones = zone_idx(zone) + 1;
> > >    -    zone->zone_start_pfn = zone_start_pfn;
> > > -
> > then how can mminit_dprintk print zone->zone_start_pfn ? always print 0 make no sense.
>
> The full code here:
>
> 	mminit_dprintk(MMINIT_TRACE, "memmap_init",
> 			"Initialising map node %d zone %lu pfns %lu -> %lu\n",
> 			pgdat->node_id,
> 			(unsigned long)zone_idx(zone),
> 			zone_start_pfn, (zone_start_pfn + size));
>
>
> It doesn't always print 0, it still behaves as I expected.
> Could you elaborate?

Yeah, you are right. I mean mminit_dprintk is called after 
zone->zone_start_pfn initialized to show initialising state, but after 
this patch applied zone->zone_start_pfn will not be initialized before 
this print point.

> Thanks,
> Lai
>
>
> > >        mminit_dprintk(MMINIT_TRACE, "memmap_init",
> > >                "Initialising map node %d zone %lu pfns %lu -> %lu\n",
> > >                pgdat->node_id,
> > > @@ -4465,6 +4463,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
> > >            ret = init_currently_empty_zone(zone, zone_start_pfn,
> > >                            size, MEMMAP_EARLY);
> > >            BUG_ON(ret);
> > > +        zone->zone_start_pfn = zone_start_pfn;
> > >            memmap_init(size, nid, j, zone_start_pfn);
> > >            zone_start_pfn += size;
> > >        }

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