[RFC PATCH 2/2] arm64: Implement vmalloc based thread_info allocator

[yalin.wang2010@gmail.com (yalin wang)]

2015-05-25 0:02 GMT+08:00 Jungseok Lee <jungseoklee85@gmail.com>:
> Fork-routine sometimes fails to get a physically contiguous region for
> thread_info on 4KB page system although free memory is enough. That is,
> a physically contiguous region, which is currently 16KB, is not available
> since system memory is fragmented.
>
> This patch tries to solve the problem as allocating thread_info memory
> from vmalloc space, not 1:1 mapping one. The downside is one additional
> page allocation in case of vmalloc. However, vmalloc space is large enough,
> around 240GB, under a combination of 39-bit VA and 4KB page. Thus, it is
> not a big tradeoff for fork-routine service.
>
> Suggested-by: Sungjinn Chung <barami97@gmail.com>
> Signed-off-by: Jungseok Lee <jungseoklee85@gmail.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: linux-kernel at vger.kernel.org
> Cc: linux-mm at kvack.org
> ---
>  arch/arm64/Kconfig                   | 12 ++++++++++++
>  arch/arm64/include/asm/thread_info.h |  9 +++++++++
>  arch/arm64/kernel/process.c          |  7 +++++++
>  3 files changed, 28 insertions(+)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 99930cf..93c236a 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -536,6 +536,18 @@ config ARCH_SELECT_MEMORY_MODEL
>  config HAVE_ARCH_PFN_VALID
>         def_bool ARCH_HAS_HOLES_MEMORYMODEL || !SPARSEMEM
>
> +config ARCH_THREAD_INFO_ALLOCATOR
> +       bool "Enable vmalloc based thread_info allocator (EXPERIMENTAL)"
> +       depends on ARM64_4K_PAGES
> +       default n
> +       help
> +         This feature enables vmalloc based thread_info allocator. It
> +         prevents fork-routine from begin failed to obtain physically
> +         contiguour region due to memory fragmentation on low system
> +         memory platforms.
> +
> +         If unsure, say N
> +
>  config HW_PERF_EVENTS
>         bool "Enable hardware performance counter support for perf events"
>         depends on PERF_EVENTS
> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
> index dcd06d1..e753e59 100644
> --- a/arch/arm64/include/asm/thread_info.h
> +++ b/arch/arm64/include/asm/thread_info.h
> @@ -61,6 +61,15 @@ struct thread_info {
>  #define init_thread_info       (init_thread_union.thread_info)
>  #define init_stack             (init_thread_union.stack)
>
> +#ifdef CONFIG_ARCH_THREAD_INFO_ALLOCATOR
> +#define alloc_thread_info_node(tsk, node)                              \
> +({                                                                     \
> +       __vmalloc_node_range(THREAD_SIZE, THREAD_SIZE, VMALLOC_START,   \
> +                       VMALLOC_END, GFP_KERNEL, PAGE_KERNEL, 0,        \
> +                       NUMA_NO_NODE, __builtin_return_address(0));     \
> +})
why not add __GFP_HIGHMEM, if you decided to use vmalloc() alloc stack pages?

Thanks