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    Subject[PATCH -v4 1/9] mm, swap: Make swap cluster size same of THP size on x86_64
    Date
    From: Huang Ying <ying.huang@intel.com>

    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 68a166d..0a29bcc 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 2210de2..18e247b 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,
    --
    2.9.3
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