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

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@google.com>

Acked-by: Cyrill Gorcunov <redacted>

Thanks a lot, Hugh!