mm, swap: make CONFIG_THP_SWAP depend on CONFIG_SWAP

CONFIG_THP_SWAP should depend on CONFIG_SWAP, because it's unreasonable
to optimize swapping for THP (Transparent Huge Page) without basic
swapping support.

In original code, when CONFIG_SWAP=n and CONFIG_THP_SWAP=y,
split_swap_cluster() will not be built because it is in swapfile.c, but
it will be called in huge_memory.c.  This doesn't trigger a build error
in practice because the call site is enclosed by PageSwapCache(), which
is defined to be constant 0 when CONFIG_SWAP=n.  But this is fragile and
should be fixed.

The comments are fixed too to reflect the latest progress.

Link: http://lkml.kernel.org/r/[email protected]
Fixes: 38d8b4e6bdc8 ("mm, THP, swap: delay splitting THP during swap out")
Signed-off-by: "Huang, Ying" <[email protected]>
Reviewed-by: Dan Williams <[email protected]>
Reviewed-by: Naoya Horiguchi <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Shaohua Li <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Zi Yan <[email protected]>
Cc: Daniel Jordan <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

diff --git a/mm/Kconfig b/mm/Kconfig
index adfeae4decb4f660a6413c9efca7d6f44f89a9ea..a550635ea5c353a8f226f7d1b429706a379a46a7 100644 (file)
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -419,10 +419,11 @@ config ARCH_WANTS_THP_SWAP
 
 config THP_SWAP
        def_bool y
-       depends on TRANSPARENT_HUGEPAGE && ARCH_WANTS_THP_SWAP
+       depends on TRANSPARENT_HUGEPAGE && ARCH_WANTS_THP_SWAP && SWAP
        help
          Swap transparent huge pages in one piece, without splitting.
-         XXX: For now this only does clustered swap space allocation.
+         XXX: For now, swap cluster backing transparent huge page
+         will be split after swapout.
 
          For selection by architectures with reasonable THP sizes.