Re: [V4 PATCH 27/27] memory,hotplug: Don't modify the zone_start_pfn outside of zone_span_writelock()

Yasuaki Ishimatsu
2012-09-11T10:19:20Z

Hi Lai,

2012/09/11 18:44, Lai Jiangshan wrote:
> On 09/11/2012 08:40 AM, Yasuaki Ishimatsu wrote:
>> Hi Lai,
>>
>> Using memory_online to hot-added node's memory, the following kernel messages
>> were shown. Is this a known issue?
>
> Fixed.
>
> Subject: Don't modify the zone_start_pfn outside of zone_span_writelock()
>
> Original __add_zone() and new online_movable/online_kernel
> maybe call sleep-able init_currently_empty_zone() to init wait_table,
>
> but this function also modifies the zone_start_pfn without lock.
> so we move this code out, and ensure the modification of zone_start_pfn is done
> with zone_span_writelock() held or booting.
>
> Since zone_start_pfn is not modified by init_currently_empty_zone()
> grow_zone_span() needs to be updated to be aware of empty zone.
>
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
> Reported-by: Yasuaki ISIMATU <isimatu.yasuaki@jp.fujitsu.com>
> Tested-by: Wen Congyang <wency@cn.fujitsu.com>

Applying the patch, the kernel messages disappeared. Thanks.
But I have a question. Using online_movable, the following messages are shown.

[ 608.314608] Built 3 zonelists in Node order, mobility grouping on. Total pages: 7844412
[ 608.411478] Policy zone: Normal

I think memory is allocated to ZONE_MOVABLE by using online_movable.
So why is "Policy zone: Normal" shown? It should be "Policy zone: Movable"

Thanks,
Yasuaki Ishimatsu

> ---
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 3ad25f9..c26a4ea 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -201,7 +201,7 @@ 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 009ac28..637b4f8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3991,8 +3991,6 @@ 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;
> -
> mminit_dprintk(MMINIT_TRACE, "memmap_init",
> "Initialising map node %d zone %lu pfns %lu -> %lu\n",
> pgdat->node_id,
> @@ -4459,6 +4457,7 @@ 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;
> }
>