[PATCH next] mm: make swapoff more robust against soft dirty

[Cyrill Gorcunov]

On Sat, Jan 09, 2016 at 04:59:42PM -0800, Hugh Dickins wrote:
> Both s390 and powerpc have hit the issue of swapoff hanging, when
> CONFIG_HAVE_ARCH_SOFT_DIRTY and CONFIG_MEM_SOFT_DIRTY ifdefs were
> not quite as x86_64 had them.  I think it would be much clearer if
> HAVE_ARCH_SOFT_DIRTY was just a Kconfig option set by architectures
> to determine whether the MEM_SOFT_DIRTY option should be offered,
> and the actual code depend upon CONFIG_MEM_SOFT_DIRTY alone.
> 
> But won't embark on that change myself: instead make swapoff more
> robust, by using pte_swp_clear_soft_dirty() on each pte it encounters,
> without an explicit #ifdef CONFIG_MEM_SOFT_DIRTY.  That being a no-op,
> whether the bit in question is defined as 0 or the asm-generic fallback
> is used, unless soft dirty is fully turned on.
> 
> Why "maybe" in maybe_same_pte()?  Rename it pte_same_as_swp().
>
> Signed-off-by: Hugh Dickins <hughd at google.com>
Acked-by: Cyrill Gorcunov <gorcunov at openvz.org>

Thanks a lot, Hugh!