[PATCH -v5 1/9] mm, swap: Make swap cluster size same of THP size on x86_64

Huang, Ying
2016-11-16T03:14:34Z

In this patch, the size of the swap cluster is changed to that of the
THP (Transparent Huge Page) on x86_64 architecture (512). This is for
the THP swap support on x86_64. Where one swap cluster will be used to
hold the contents of each THP swapped out. And some information of the
swapped out THP (such as compound map count) will be recorded in the
swap_cluster_info data structure.

For other architectures which want THP swap support,
ARCH_USES_THP_SWAP_CLUSTER need to be selected in the Kconfig file for
the architecture.

In effect, this will enlarge swap cluster size by 2 times on x86_64.
Which may make it harder to find a free cluster when the swap space
becomes fragmented. So that, this may reduce the continuous swap space
allocation and sequential write in theory. The performance test in 0day
shows no regressions caused by this.

Cc: Hugh Dickins <hughd@google.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
arch/x86/Kconfig | 1 +
mm/Kconfig | 13 +++++++++++++
mm/swapfile.c | 4 ++++
3 files changed, 18 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 8b93519..59dc488 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -165,6 +165,7 @@ config X86
select HAVE_STACK_VALIDATION if X86_64
select ARCH_USES_HIGH_VMA_FLAGS if X86_INTEL_MEMORY_PROTECTION_KEYS
select ARCH_HAS_PKEYS if X86_INTEL_MEMORY_PROTECTION_KEYS
+ select ARCH_USES_THP_SWAP_CLUSTER if X86_64

config INSTRUCTION_DECODER
def_bool y
diff --git a/mm/Kconfig b/mm/Kconfig
index 86e3e0e..5a63c87 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -503,6 +503,19 @@ config FRONTSWAP

If unsure, say Y to enable frontswap.

+config ARCH_USES_THP_SWAP_CLUSTER
+ bool
+ default n
+
+config THP_SWAP_CLUSTER
+ bool
+ depends on SWAP && TRANSPARENT_HUGEPAGE && ARCH_USES_THP_SWAP_CLUSTER
+ default y
+ help
+ Use one swap cluster to hold the contents of the THP
+ (Transparent Huge Page) swapped out. The size of the swap
+ cluster will be same as that of THP.
+
config CMA
bool "Contiguous Memory Allocator"
depends on HAVE_MEMBLOCK && MMU
diff --git a/mm/swapfile.c b/mm/swapfile.c
index f304389..34888e5b 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -196,7 +196,11 @@ static void discard_swap_cluster(struct swap_info_struct *si,
}
}

+#ifdef CONFIG_THP_SWAP_CLUSTER
+#define SWAPFILE_CLUSTER HPAGE_PMD_NR
+#else
#define SWAPFILE_CLUSTER 256
+#endif
#define LATENCY_LIMIT 256

static inline void cluster_set_flag(struct swap_cluster_info *info,
--
2.10.2