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    SubjectRe: [PATCH 3/3] memory_hotplug: Don't modify the zone_start_pfn outside of zone_span_writelock()
    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@csn.ul.ie>
    >>> 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>
    >>> ---
    >>> 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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