[PATCH v2 3/3] powerpc: Kconfig: Enable THP_SWAP on Book3S64

["Ritesh Harjani (IBM)" <ritesh.list@gmail.com>]

THP_SWAP avoids splitting of a transparent huge folio into 32 smaller
64K folios (Radix-64K pagesize / 2M PMD) or into 256 smaller 64K folios
(Hash-64K pagesize / 16M PMD), during swapout. This improves the
swapping performance since all the bookking & I/O submission happens
once per large folio. More details at [1].

PowerPC Book3S64 could not enable this before because PMD_ORDER is
selected at runtime depending upon the chosen MMU. The earlier patches
in this series turn SWAPFILE_CLUSTER into a runtime value and introduce
an ARCH_MAX_PMD_ORDER upperbound override for SWAP_NR_ORDERS. With those
changes, we can now enable THP SWAP for Book3S64.

This increases bandwidth throughput with zram backend for swapout by
40-50% with Radix and 100-130% with Hash (Tested by Sayali)

[1]: https://lore.kernel.org/all/20170515112522.32457-2-ying.huang@intel.com/

Tested-by: Sayali Patil <sayalip@linux.ibm.com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 arch/powerpc/platforms/Kconfig.cputype | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/powerpc/platforms/Kconfig.cputype b/arch/powerpc/platforms/Kconfig.cputype
index bac02c83bb3e..48f74bd22343 100644
--- a/arch/powerpc/platforms/Kconfig.cputype
+++ b/arch/powerpc/platforms/Kconfig.cputype
@@ -113,6 +113,7 @@ config PPC_THP
        select HAVE_ARCH_TRANSPARENT_HUGEPAGE
        select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
        select ARCH_ENABLE_THP_MIGRATION if TRANSPARENT_HUGEPAGE
+       select ARCH_WANTS_THP_SWAP	if TRANSPARENT_HUGEPAGE

 choice
 	prompt "CPU selection"
--
2.39.5