mm: fix mapcount mismatch in hugepage migration

try_to_unmap_one() should be able to handle hugetlb, but page_remove_rmap()
in that function takes false as a compound flag, which breaks hugepage migration
with the following message.

  Soft offlining page 0x1d4a00 at 0x7ff634a00000
  soft offline: 0x1d4a00: migration failed 1, type 60000000000401c
  BUG: Bad page state in process sysctl  pfn:1d4a00
  page:ffffea0007528000 count:0 mapcount:0 mapping:          (null) index:0x0 compound_mapcount: 10
  flags: 0x600000000004008(uptodate|head)
  page dumped because: nonzero mapcount
  Modules linked in: cfg80211 rfkill crc32c_intel virtio_balloon serio_raw i2c_piix4 virtio_blk virtio_net ata_generic pata_acpi
  CPU: 3 PID: 11882 Comm: sysctl Tainted: G        W       4.3.0-mmotm-2015-11-10-15-53-151112-1812-00015-53+ torvalds#240
  Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
   ffffffff81a1a124 ffff8800da047bd0 ffffffff81340adf ffffea0007528000
   ffff8800da047bf8 ffffffff8116e206 0000000000000009 ffffffff81f72538
   ffffea0007528000 ffff8800da047c48 ffffffff8116e6d6 0000020000000000
  Call Trace:
   [<ffffffff81340adf>] dump_stack+0x44/0x55
   [<ffffffff8116e206>] bad_page+0xc6/0x110
   [<ffffffff8116e6d6>] free_pages_prepare+0x486/0x500
   [<ffffffff81170f9a>] __free_pages_ok+0x1a/0xb0
   [<ffffffff81171af1>] __free_pages+0x21/0x40
   [<ffffffff811b5d79>] update_and_free_page+0xa9/0x230
   [<ffffffff811b6641>] free_pool_huge_page+0xc1/0xe0
   [<ffffffff811b6d02>] set_max_huge_pages+0x382/0x4d0
   [<ffffffff811b7002>] hugetlb_sysctl_handler_common+0xa2/0xd0
   [<ffffffff811b823e>] hugetlb_sysctl_handler+0x1e/0x20
   [<ffffffff812535fe>] proc_sys_call_handler+0xae/0xc0
   [<ffffffff81253624>] proc_sys_write+0x14/0x20
   [<ffffffff811e8758>] __vfs_write+0x28/0xe0
   [<ffffffff810d1864>] ? percpu_down_read+0x14/0x60
   [<ffffffff811e8d29>] vfs_write+0xa9/0x190
   [<ffffffff811e9646>] SyS_write+0x46/0xb0
   [<ffffffff8163d797>] entry_SYSCALL_64_fastpath+0x12/0x6a

This patch simply fixes this by giving the compound flag via PageHuge.

Fixes: "rmap: add argument to charge compound page".

Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/rmap.c

@@ -1430,7 +1430,7 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
  } else
  dec_mm_counter(mm, mm_counter_file(page));
 
- page_remove_rmap(page, false);
+ page_remove_rmap(page, PageHuge(page));
  page_cache_release(page);
 
 out_unmap: