Hi David,

I love your patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on linux/master v5.5-rc1 next-20191209]
[cannot apply to mmotm/master]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/David-Hildenbrand/mm-fix-max_pfn-not-falling-on-section-boundary/20191210-071011
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 6794862a16ef41f753abd75c03a152836e4c8028
config: i386-defconfig (attached as .config)
compiler: gcc-7 (Debian 7.5.0-1) 7.5.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

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

All errors (new ones prefixed by >>):

   In file included from include/asm-generic/bug.h:19:0,
                    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 include/linux/memblock.h:13,
                    from fs/proc/page.c:2:
   fs/proc/page.c: In function 'kpagecount_read':
>> fs/proc/page.c:32:55: error: 'PAGES_PER_SECTION' undeclared (first use in this function); did you mean 'PAGE_KERNEL_IO'?
     const unsigned long max_dump_pfn = round_up(max_pfn, PAGES_PER_SECTION);
                                                          ^
   include/linux/kernel.h:62:46: note: in definition of macro '__round_mask'
    #define __round_mask(x, y) ((__typeof__(x))((y)-1))
                                                 ^
   fs/proc/page.c:32:37: note: in expansion of macro 'round_up'
     const unsigned long max_dump_pfn = round_up(max_pfn, PAGES_PER_SECTION);
                                        ^~~~~~~~
   fs/proc/page.c:32:55: note: each undeclared identifier is reported only once for each function it appears in
     const unsigned long max_dump_pfn = round_up(max_pfn, PAGES_PER_SECTION);
                                                          ^
   include/linux/kernel.h:62:46: note: in definition of macro '__round_mask'
    #define __round_mask(x, y) ((__typeof__(x))((y)-1))
                                                 ^
   fs/proc/page.c:32:37: note: in expansion of macro 'round_up'
     const unsigned long max_dump_pfn = round_up(max_pfn, PAGES_PER_SECTION);
                                        ^~~~~~~~
   fs/proc/page.c: In function 'kpageflags_read':
   fs/proc/page.c:212:55: error: 'PAGES_PER_SECTION' undeclared (first use in this function); did you mean 'PAGE_KERNEL_IO'?
     const unsigned long max_dump_pfn = round_up(max_pfn, PAGES_PER_SECTION);
                                                          ^
   include/linux/kernel.h:62:46: note: in definition of macro '__round_mask'
    #define __round_mask(x, y) ((__typeof__(x))((y)-1))
                                                 ^
   fs/proc/page.c:212:37: note: in expansion of macro 'round_up'
     const unsigned long max_dump_pfn = round_up(max_pfn, PAGES_PER_SECTION);
                                        ^~~~~~~~

vim +32 fs/proc/page.c

   > 2	#include <linux/memblock.h>
     3	#include <linux/compiler.h>
     4	#include <linux/fs.h>
     5	#include <linux/init.h>
     6	#include <linux/ksm.h>
     7	#include <linux/mm.h>
     8	#include <linux/mmzone.h>
     9	#include <linux/huge_mm.h>
    10	#include <linux/proc_fs.h>
    11	#include <linux/seq_file.h>
    12	#include <linux/hugetlb.h>
    13	#include <linux/memcontrol.h>
    14	#include <linux/mmu_notifier.h>
    15	#include <linux/page_idle.h>
    16	#include <linux/kernel-page-flags.h>
    17	#include <linux/uaccess.h>
    18	#include "internal.h"
    19	
    20	#define KPMSIZE sizeof(u64)
    21	#define KPMMASK (KPMSIZE - 1)
    22	#define KPMBITS (KPMSIZE * BITS_PER_BYTE)
    23	
    24	/* /proc/kpagecount - an array exposing page counts
    25	 *
    26	 * Each entry is a u64 representing the corresponding
    27	 * physical page count.
    28	 */
    29	static ssize_t kpagecount_read(struct file *file, char __user *buf,
    30				     size_t count, loff_t *ppos)
    31	{
  > 32		const unsigned long max_dump_pfn = round_up(max_pfn, PAGES_PER_SECTION);
    33		u64 __user *out = (u64 __user *)buf;
    34		struct page *ppage;
    35		unsigned long src = *ppos;
    36		unsigned long pfn;
    37		ssize_t ret = 0;
    38		u64 pcount;
    39	
    40		pfn = src / KPMSIZE;
    41		if (src & KPMMASK || count & KPMMASK)
    42			return -EINVAL;
    43		if (src >= max_dump_pfn * KPMSIZE)
    44			return 0;
    45		count = min_t(unsigned long, count, (max_dump_pfn * KPMSIZE) - src);
    46	
    47		while (count > 0) {
    48			/*
    49			 * TODO: ZONE_DEVICE support requires to identify
    50			 * memmaps that were actually initialized.
    51			 */
    52			ppage = pfn_to_online_page(pfn);
    53	
    54			if (!ppage || PageSlab(ppage) || page_has_type(ppage))
    55				pcount = 0;
    56			else
    57				pcount = page_mapcount(ppage);
    58	
    59			if (put_user(pcount, out)) {
    60				ret = -EFAULT;
    61				break;
    62			}
    63	
    64			pfn++;
    65			out++;
    66			count -= KPMSIZE;
    67	
    68			cond_resched();
    69		}
    70	
    71		*ppos += (char __user *)out - buf;
    72		if (!ret)
    73			ret = (char __user *)out - buf;
    74		return ret;
    75	}
    76	

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