Barry Song <21cnbao@xxxxxxxxx> writes:
> From: Barry Song <v-songbaohua@xxxxxxxx>
>
> 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@xxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Hugh Dickins <hughd@xxxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> Cc: Steven Price <steven.price@xxxxxxx>
> Cc: Yang Shi <shy828301@xxxxxxxxx>
> Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
> ---
> -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;
> }
