On 7/19/22 08:58, Huang, Ying wrote:
> Anshuman Khandual <anshuman.khandual@xxxxxxx> writes:
>
>> On 7/19/22 06:53, Barry Song wrote:
>>> On Tue, Jul 19, 2022 at 12:44 PM Huang, Ying <ying.huang@xxxxxxxxx> wrote:
>>>>
>>>> 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);
>>>> }
>>>
>>> This looks good. then i'll need to change arm64 to
>>>
>>> +static inline bool arch_thp_swp_supported(void)
>>> +{
>>> + return IS_ENABLED(ARCH_WANTS_THP_SWAP) && !system_supports_mte();
>>> +}
>>
>> Why ? CONFIG_THP_SWAP depends on ARCH_WANTS_THP_SWAP. In folio_alloc_swap(),
>> IS_ENABLED(CONFIG_THP_SWAP) enabled, will also imply ARCH_WANTS_THP_SWAP too
>> is enabled. Hence checking for ARCH_WANTS_THP_SWAP again does not make sense
>> either in the generic fallback stub, or in arm64 platform override. Because
>> without ARCH_WANTS_THP_SWAP enabled, arch_thp_swp_supported() should never
>> be called in the first place.
>
> For the only caller now, the checking looks redundant. But the original
> proposed implementation as follows,
>
> static inline bool arch_thp_swp_supported(void)
> {
> return true;
> }
>
> will return true even on architectures that don't support/want THP swap.
But the function will never be called on for those platforms.
> That will confuse people too.
I dont see how.
>
> And the "redundant" checking has no run time overhead, because compiler
> will do the trick.
I understand that, but dont think this indirection is necessary.
