From: Huang Ying <ying.huang@xxxxxxxxx> Subject: 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/20180713021228.439-1-ying.huang@xxxxxxxxx Fixes: 38d8b4e6bdc8 ("mm, THP, swap: delay splitting THP during swap out") Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx> Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx> Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Shaohua Li <shli@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Minchan Kim <minchan@xxxxxxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: Zi Yan <zi.yan@xxxxxxxxxxxxxx> Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/Kconfig | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/mm/Kconfig~mm-swap-make-config_thp_swap-depends-on-config_swap +++ a/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. _
