Re: [PATCH -v3 01/10] mm, swap: Make swap cluster size same of THP size on x86_64

From: Kirill A. Shutemov
Date: Thu Sep 08 2016 - 07:07:38 EST


On Wed, Sep 07, 2016 at 09:46:00AM -0700, Huang, Ying wrote:
> From: Huang Ying <ying.huang@xxxxxxxxx>
>
> 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, 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@xxxxxxxxxx>
> Cc: Shaohua Li <shli@xxxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Suggested-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> ---
> 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 4c39728..421d862 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -164,6 +164,7 @@ 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 be0ee11..2da8128 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 8f1b97d..4b78402 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_SIZE / PAGE_SIZE)

#define SWAPFILE_CLUSTER HPAGE_PMD_NR

Note, HPAGE_SIZE is not nessesary HPAGE_PMD_SIZE. I can imagine an arch
with multiple huge page sizes where HPAGE_SIZE differs from what is used
for THP.

> +#else
> #define SWAPFILE_CLUSTER 256
> +#endif
> #define LATENCY_LIMIT 256
>
> static inline void cluster_set_flag(struct swap_cluster_info *info,
> --
> 2.8.1
>

--
Kirill A. Shutemov