Re: [RESEND PATCH v3] arm64: enable THP_SWAP for arm64

["Huang, Ying" <ying.huang@intel.com>]

Barry Song <21cnbao@gmail.com> writes:

> From: Barry Song <v-songbaohua@oppo.com>
>
> THP_SWAP has been proven to improve the swap throughput significantly
> on x86_64 according to commit bd4c82c22c367e ("mm, THP, swap: delay
> splitting THP after swapped out").
> As long as arm64 uses 4K page size, it is quite similar with x86_64
> by having 2MB PMD THP. THP_SWAP is architecture-independent, thus,
> enabling it on arm64 will benefit arm64 as well.
> A corner case is that MTE has an assumption that only base pages
> can be swapped. We won't enable THP_SWAP for ARM64 hardware with
> MTE support until MTE is reworked to coexist with THP_SWAP.
>
> A micro-benchmark is written to measure thp swapout throughput as
> below,
>
>  unsigned long long tv_to_ms(struct timeval tv)
>  {
>  	return tv.tv_sec * 1000 + tv.tv_usec / 1000;
>  }
>
>  main()
>  {
>  	struct timeval tv_b, tv_e;;
>  #define SIZE 400*1024*1024
>  	volatile void *p = mmap(NULL, SIZE, PROT_READ | PROT_WRITE,
>  				MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>  	if (!p) {
>  		perror("fail to get memory");
>  		exit(-1);
>  	}
>
>  	madvise(p, SIZE, MADV_HUGEPAGE);
>  	memset(p, 0x11, SIZE); /* write to get mem */
>
>  	gettimeofday(&tv_b, NULL);
>  	madvise(p, SIZE, MADV_PAGEOUT);
>  	gettimeofday(&tv_e, NULL);
>
>  	printf("swp out bandwidth: %ld bytes/ms\n",
>  			SIZE/(tv_to_ms(tv_e) - tv_to_ms(tv_b)));
>  }
>
> Testing is done on rk3568 64bit quad core processor Quad Core
> Cortex-A55 platform - ROCK 3A.
> thp swp throughput w/o patch: 2734bytes/ms (mean of 10 tests)
> thp swp throughput w/  patch: 3331bytes/ms (mean of 10 tests)
>
> Cc: "Huang, Ying" <ying.huang@intel.com>
> Cc: Minchan Kim <minchan@kernel.org>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Andrea Arcangeli <aarcange@redhat.com>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: Steven Price <steven.price@arm.com>
> Cc: Yang Shi <shy828301@gmail.com>
> Signed-off-by: Barry Song <v-songbaohua@oppo.com>
> ---
>  -v3: 
>  * refine the commit log;
>  * add a benchmark result;
>  * refine the macro of arch_thp_swp_supported
>  Thanks to the comments of Anshuman, Andrew, Steven
>
>  arch/arm64/Kconfig               |  1 +
>  arch/arm64/include/asm/pgtable.h |  6 ++++++
>  include/linux/huge_mm.h          | 12 ++++++++++++
>  mm/swap_slots.c                  |  2 +-
>  4 files changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 1652a9800ebe..e1c540e80eec 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -101,6 +101,7 @@ config ARM64
>  	select ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
>  	select ARCH_WANT_LD_ORPHAN_WARN
>  	select ARCH_WANTS_NO_INSTR
> +	select ARCH_WANTS_THP_SWAP if ARM64_4K_PAGES
>  	select ARCH_HAS_UBSAN_SANITIZE_ALL
>  	select ARM_AMBA
>  	select ARM_ARCH_TIMER
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 0b6632f18364..78d6f6014bfb 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -45,6 +45,12 @@
>  	__flush_tlb_range(vma, addr, end, PUD_SIZE, false, 1)
>  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>  
> +static inline bool arch_thp_swp_supported(void)
> +{
> +	return !system_supports_mte();
> +}
> +#define arch_thp_swp_supported arch_thp_swp_supported
> +
>  /*
>   * Outside of a few very special situations (e.g. hibernation), we always
>   * use broadcast TLB invalidation instructions, therefore a spurious page
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index de29821231c9..4ddaf6ad73ef 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -461,4 +461,16 @@ static inline int split_folio_to_list(struct folio *folio,
>  	return split_huge_page_to_list(&folio->page, list);
>  }
>  
> +/*
> + * archs that select ARCH_WANTS_THP_SWAP but don't support THP_SWP due to
> + * limitations in the implementation like arm64 MTE can override this to
> + * false
> + */
> +#ifndef arch_thp_swp_supported
> +static inline bool arch_thp_swp_supported(void)
> +{
> +	return true;
> +}

How about the following?

static inline bool arch_wants_thp_swap(void)
{
     return IS_ENABLED(ARCH_WANTS_THP_SWAP);
}

Best Regards,
Huang, Ying

> +#endif
> +
>  #endif /* _LINUX_HUGE_MM_H */
> diff --git a/mm/swap_slots.c b/mm/swap_slots.c
> index 2a65a89b5b4d..10b94d64cc25 100644
> --- a/mm/swap_slots.c
> +++ b/mm/swap_slots.c
> @@ -307,7 +307,7 @@ swp_entry_t folio_alloc_swap(struct folio *folio)
>  	entry.val = 0;
>  
>  	if (folio_test_large(folio)) {
> -		if (IS_ENABLED(CONFIG_THP_SWAP))
> +		if (IS_ENABLED(CONFIG_THP_SWAP) && arch_thp_swp_supported())
>  			get_swap_pages(1, &entry, folio_nr_pages(folio));
>  		goto out;
>  	}