Re: [PATCH v1] mm: fix mapcount mismatch in hugepage migration

[Kirill A. Shutemov]

On Fri, Nov 13, 2015 at 09:44:29AM +0900, Naoya Horiguchi wrote:
> 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+ #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.
> ---
> # This patch is against mmotm-2015-11-10-15-53 as a fix for "rmap: add argument
> # to charge compound page".
> 
> Signed-off-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>

Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

-- 
 Kirill A. Shutemov
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