Hi David,

I love your patch! Perhaps something to improve:

[auto build test WARNING on mmotm/master]

url:    https://github.com/0day-ci/linux/commits/David-Hildenbrand/mm-memory_hotplug-Shrink-zones-before-removing-memory/20191002-054310
base:   git://git.cmpxchg.org/linux-mmotm.git master
config: x86_64-randconfig-b002-201939 (attached as .config)
compiler: gcc-7 (Debian 7.4.0-13) 7.4.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   In file included from include/asm-generic/bug.h:5:0,
                    from arch/x86/include/asm/bug.h:83,
                    from include/linux/bug.h:5,
                    from include/linux/mmdebug.h:5,
                    from include/linux/mm.h:9,
                    from mm/memory_hotplug.c:9:
   mm/memory_hotplug.c: In function '__remove_zone':
   mm/memory_hotplug.c:471:24: error: 'ZONE_DEVICE' undeclared (first use in this function); did you mean 'ZONE_MOVABLE'?
     if (zone_idx(zone) == ZONE_DEVICE)
                           ^
   include/linux/compiler.h:58:52: note: in definition of macro '__trace_if_var'
    #define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond))
                                                       ^~~~
>> mm/memory_hotplug.c:471:2: note: in expansion of macro 'if'
     if (zone_idx(zone) == ZONE_DEVICE)
     ^~
   mm/memory_hotplug.c:471:24: note: each undeclared identifier is reported only once for each function it appears in
     if (zone_idx(zone) == ZONE_DEVICE)
                           ^
   include/linux/compiler.h:58:52: note: in definition of macro '__trace_if_var'
    #define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond))
                                                       ^~~~
>> mm/memory_hotplug.c:471:2: note: in expansion of macro 'if'
     if (zone_idx(zone) == ZONE_DEVICE)
     ^~

vim +/if +471 mm/memory_hotplug.c

   459	
   460	static void __remove_zone(struct zone *zone, unsigned long start_pfn,
   461			unsigned long nr_pages)
   462	{
   463		struct pglist_data *pgdat = zone->zone_pgdat;
   464		unsigned long flags;
   465	
   466		/*
   467		 * Zone shrinking code cannot properly deal with ZONE_DEVICE. So
   468		 * we will not try to shrink the zones - which is okay as
   469		 * set_zone_contiguous() cannot deal with ZONE_DEVICE either way.
   470		 */
 > 471		if (zone_idx(zone) == ZONE_DEVICE)
   472			return;
   473	
   474		pgdat_resize_lock(zone->zone_pgdat, &flags);
   475		shrink_zone_span(zone, start_pfn, start_pfn + nr_pages);
   476		update_pgdat_span(pgdat);
   477		pgdat_resize_unlock(zone->zone_pgdat, &flags);
   478	}
   479	

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