bio_iov_iter_get_pages() + page_alloc.shuffle=1 migrating failures

[Qian Cai]

Memory offline [1] starts to fail on linux-next on ppc64le with
page_alloc.shuffle=1 where the "echo offline" command hangs with lots of
migrating failures below. It seems in migrate_page_move_mapping()

	if (!mapping) {
		/* Anonymous page without mapping */
		if (page_count(page) != expected_count)
			return -EAGAIN;

It expected count=1 but actual count=2.

There are two ways to make the problem go away. One is to remove this line in
__shuffle_free_memory(),

	shuffle_zone(z);

The other is reverting some bio commits. Bisecting so far indicates the culprit
is in one of those (the 3rd commit looks more suspicious than the others).

block: only allow contiguous page structs in a bio_vec
block: don't allow multiple bio_iov_iter_get_pages calls per bio
block: change how we get page references in bio_iov_iter_get_pages

[  446.578064] migrating pfn 2003d5eaa failed ret:22
[  446.578066] page:c00a00800f57aa80 count:2 mapcount:0 mapping:c000001db4c827e9
index:0x13c08a
[  446.578220] anon
[  446.578222] flags: 0x83fffc00008002e(referenced|uptodate|dirty|active|swapbacked)
[  446.578347] raw: 083fffc00008002e c00a00800f57f808 c00a00800f579f88
c000001db4c827e9
[  446.944807] raw: 000000000013c08a 0000000000000000 00000002ffffffff
c00020141a738008
[  446.944883] page dumped because: migration failure
[  446.944948] page->mem_cgroup:c00020141a738008
[  446.945024] page allocated via order 0, migratetype Movable, gfp_mask
0x100cca(GFP_HIGHUSER_MOVABLE)
[  446.945148]  prep_new_page+0x390/0x3a0
[  446.945228]  get_page_from_freelist+0xd9c/0x1bf0
[  446.945292]  __alloc_pages_nodemask+0x1cc/0x1780
[  446.945335]  alloc_pages_vma+0xc0/0x360
[  446.945401]  do_anonymous_page+0x244/0xb20
[  446.945472]  __handle_mm_fault+0xcf8/0xfb0
[  446.945532]  handle_mm_fault+0x1c0/0x2b0
[  446.945615]  __get_user_pages+0x3ec/0x690
[  446.945652]  get_user_pages_unlocked+0x104/0x2f0
[  446.945693]  get_user_pages_fast+0xb0/0x200
[  446.945762]  iov_iter_get_pages+0xf4/0x6a0
[  446.945802]  bio_iov_iter_get_pages+0xc0/0x450
[  446.945876]  blkdev_direct_IO+0x2e0/0x630
[  446.945941]  generic_file_read_iter+0xbc/0x230
[  446.945990]  blkdev_read_iter+0x50/0x80
[  446.946031]  aio_read+0x128/0x1d0
[  446.946082] migrating pfn 2003d5fe0 failed ret:22
[  446.946084] page:c00a00800f57f800 count:2 mapcount:0 mapping:c000001db4c827e9
index:0x13c19e
[  446.946239] anon
[  446.946241] flags: 0x83fffc00008002e(referenced|uptodate|dirty|active|swapbacked)
[  446.946384] raw: 083fffc00008002e c000200deb3dfa28 c00a00800f57aa88
c000001db4c827e9
[  446.946497] raw: 000000000013c19e 0000000000000000 00000002ffffffff
c00020141a738008
[  446.946605] page dumped because: migration failure
[  446.946662] page->mem_cgroup:c00020141a738008
[  446.946724] page allocated via order 0, migratetype Movable, gfp_mask
0x100cca(GFP_HIGHUSER_MOVABLE)
[  446.946846]  prep_new_page+0x390/0x3a0
[  446.946899]  get_page_from_freelist+0xd9c/0x1bf0
[  446.946959]  __alloc_pages_nodemask+0x1cc/0x1780
[  446.947047]  alloc_pages_vma+0xc0/0x360
[  446.947101]  do_anonymous_page+0x244/0xb20
[  446.947143]  __handle_mm_fault+0xcf8/0xfb0
[  446.947200]  handle_mm_fault+0x1c0/0x2b0
[  446.947256]  __get_user_pages+0x3ec/0x690
[  446.947306]  get_user_pages_unlocked+0x104/0x2f0
[  446.947366]  get_user_pages_fast+0xb0/0x200
[  446.947458]  iov_iter_get_pages+0xf4/0x6a0
[  446.947515]  bio_iov_iter_get_pages+0xc0/0x450
[  446.947588]  blkdev_direct_IO+0x2e0/0x630
[  446.947636]  generic_file_read_iter+0xbc/0x230
[  446.947703]  blkdev_read_iter+0x50/0x80
[  446.947758]  aio_read+0x128/0x1d0

[1]
i=0
found=0
for mem in $(ls -d /sys/devices/system/memory/memory*); do
        i=$((i + 1))
        echo "iteration: $i"
        echo offline > $mem/state
        if [ $? -eq 0 ] && [ $found -eq 0 ]; then
                found=1
                continue
        fi
        echo online > $mem/state
done