linux-kernel - [PATCH v3] riscv: enable THP

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Message-Id: <20220829145742.3139-1-jszhang@kernel.org>
Date:   Mon, 29 Aug 2022 22:57:42 +0800
From:   Jisheng Zhang <jszhang@...nel.org>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>
Cc:     linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Andrew Jones <ajones@...tanamicro.com>,
        Conor Dooley <conor.dooley@...rochip.com>
Subject: [PATCH v3] riscv: enable THP_SWAP for RV64

I have a Sipeed Lichee RV dock board which only has 512MB DDR, so
memory optimizations such as swap on zram are helpful. As is seen
in commit d0637c505f8a ("arm64: enable THP_SWAP for arm64") and
commit bd4c82c22c367e ("mm, THP, swap: delay splitting THP after
swapped out"), THP_SWAP can improve the swap throughput significantly.

Enable THP_SWAP for RV64, testing the micro-benchmark which is
introduced by commit d0637c505f8a ("arm64: enable THP_SWAP for arm64")
shows below numbers on the Lichee RV dock board:

swp out bandwidth w/o patch: 66908 bytes/ms (mean of 10 tests)
swp out bandwidth w/ patch: 322638 bytes/ms (mean of 10 tests)

Improved by 382%!

Signed-off-by: Jisheng Zhang <jszhang@...nel.org>
Reviewed-by: Andrew Jones <ajones@...tanamicro.com>
Reviewed-by: Conor Dooley <conor.dooley@...rochip.com>
---
Since v2:
 - correct reviewed-by tag
 - update commit msg

Since v1:
 - collect reviewed-by tag
 - make ARCH_WANTS_THP_SWAP rely on HAVE_ARCH_TRANSPARENT_HUGEPAGE
   instead

 arch/riscv/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index ed66c31e4655..79e52441e18b 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -45,6 +45,7 @@ config RISCV
 	select ARCH_WANT_FRAME_POINTERS
 	select ARCH_WANT_GENERAL_HUGETLB
 	select ARCH_WANT_HUGE_PMD_SHARE if 64BIT
+	select ARCH_WANTS_THP_SWAP if HAVE_ARCH_TRANSPARENT_HUGEPAGE
 	select BINFMT_FLAT_NO_DATA_START_OFFSET if !MMU
 	select BUILDTIME_TABLE_SORT if MMU
 	select CLONE_BACKWARDS
-- 
2.34.1