percpu: adjust the value of PERCPU_DYNAMIC_EARLY_SIZE

LKP reported a build failure as below on the following patch "mm/slub,
percpu: correct the calculation of early percpu allocation size"

~~~~~~
In file included from <command-line>:
In function 'alloc_kmem_cache_cpus',
   inlined from 'kmem_cache_open' at mm/slub.c:4340:6:
>> >> include/linux/compiler_types.h:357:45: error: call to '__compiletime_assert_474' declared with attribute error:
BUILD_BUG_ON failed: PERCPU_DYNAMIC_EARLY_SIZE < NR_KMALLOC_TYPES * KMALLOC_SHIFT_HIGH * sizeof(struct kmem_cache_cpu)
     357 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
~~~~~~

From the kernel config file provided by LKP, the building was made on
arm64 with below Kconfig item enabled:

  CONFIG_ZONE_DMA=y
  CONFIG_SLUB_CPU_PARTIAL=y
  CONFIG_DEBUG_LOCK_ALLOC=y
  CONFIG_SLUB_STATS=y
  CONFIG_ARM64_PAGE_SHIFT=16
  CONFIG_ARM64_64K_PAGES=y

Then we will have:
  NR_KMALLOC_TYPES:4
  KMALLOC_SHIFT_HIGH:17
  sizeof(struct kmem_cache_cpu):184

The product of them is 12512, which is bigger than PERCPU_DYNAMIC_EARLY_SIZE,
12K. Hence, the BUILD_BUG_ON in alloc_kmem_cache_cpus() is triggered.

Earlier, in commit 099a19d9 ("percpu: allow limited allocation
before slab is online"), PERCPU_DYNAMIC_EARLY_SIZE was introduced and
set to 12K which is equal to the then PERPCU_DYNAMIC_RESERVE.
Later, in commit 1a4d7607 ("percpu: implement asynchronous chunk
population"), PERPCU_DYNAMIC_RESERVE was increased by 8K, while
PERCPU_DYNAMIC_EARLY_SIZE was kept unchanged.

So, here increase PERCPU_DYNAMIC_EARLY_SIZE by 8K too to accommodate to
the slub's requirement.
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Baoquan He <bhe@redhat.com>
Acked-by: Dennis Zhou <dennis@kernel.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

include/linux/percpu.h

@@ -42,7 +42,7 @@
  * larger than PERCPU_DYNAMIC_EARLY_SIZE.
  */
 #define PERCPU_DYNAMIC_EARLY_SLOTS	128
-#define PERCPU_DYNAMIC_EARLY_SIZE	(12 << 10)
+#define PERCPU_DYNAMIC_EARLY_SIZE	(20 << 10)
 
 /*
  * PERCPU_DYNAMIC_RESERVE indicates the amount of free area to piggy