Re: [PATCH v2] mm/mm_init: use node's number of cpus in deferred_page_init_max_threads

Mike Rapoport
2024-05-23T15:01:51Z

On Wed, May 22, 2024 at 04:38:01PM -0400, Eric Chanudet wrote:
> x86_64 is already using the node's cpu as maximum threads. Make that the
> default for all archs setting DEFERRED_STRUCT_PAGE_INIT.
>
> This returns to the behavior prior making the function arch-specific
> with commit ecd096506922 ("mm: make deferred init's max threads
> arch-specific").
>
> Signed-off-by: Eric Chanudet <echanude@redhat.com>
>
> ---
> Setting DEFERRED_STRUCT_PAGE_INIT and testing on a few arm64 platforms
> shows faster deferred_init_memmap completions:
>
> | | x13s | SA8775p-ride | Ampere R137-P31 | Ampere HR330 |
> | | Metal, 32GB | VM, 36GB | VM, 58GB | Metal, 128GB |
> | | 8cpus | 8cpus | 8cpus | 32cpus |
> |---------|-------------|--------------|-----------------|--------------|
> | threads | ms (%) | ms (%) | ms (%) | ms (%) |
> |---------|-------------|--------------|-----------------|--------------|
> | 1 | 108 (0%) | 72 (0%) | 224 (0%) | 324 (0%) |
> | cpus | 24 (-77%) | 36 (-50%) | 40 (-82%) | 56 (-82%) |
>
> - v1: https://lore.kernel.org/linux-arm-kernel/20240520231555.395979-5-echanude@redhat.com
> - Changes since v1:
> - Make the generic function return the number of cpus of the node as
> max threads limit instead overriding it for arm64.
> - Drop Baoquan He's R-b on v1 since the logic changed.
> - Add CCs according to patch changes (ppc and s390 set
> DEFERRED_STRUCT_PAGE_INIT by default).
>
> arch/x86/mm/init_64.c | 12 ------------
> mm/mm_init.c | 2 +-
> 2 files changed, 1 insertion(+), 13 deletions(-)
>
> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
> index 7e177856ee4f..adec42928ec1 100644
> --- a/arch/x86/mm/init_64.c
> +++ b/arch/x86/mm/init_64.c
> @@ -1354,18 +1354,6 @@ void __init mem_init(void)
> preallocate_vmalloc_pages();
> }
>
> -#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
> -int __init deferred_page_init_max_threads(const struct cpumask *node_cpumask)
> -{
> - /*
> - * More CPUs always led to greater speedups on tested systems, up to
> - * all the nodes' CPUs. Use all since the system is otherwise idle
> - * now.
> - */
> - return max_t(int, cpumask_weight(node_cpumask), 1);
> -}
> -#endif
> -
> int kernel_set_to_readonly;
>
> void mark_rodata_ro(void)
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index f72b852bd5b8..e0023aa68555 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -2126,7 +2126,7 @@ deferred_init_memmap_chunk(unsigned long start_pfn, unsigned long end_pfn,
> __weak int __init

If s390 folks confirm there's no regression for them I think we can make
this static.

> deferred_page_init_max_threads(const struct cpumask *node_cpumask)
> {
> - return 1;
> + return max_t(int, cpumask_weight(node_cpumask), 1);
> }
>
> /* Initialise remaining memory on a node */
> --
> 2.44.0
>

--
Sincerely yours,
Mike.