On 7/20/22 07:16, Barry Song wrote:
> On Tue, Jul 19, 2022 at 4:04 PM Anshuman Khandual
> <anshuman.khandual@xxxxxxx> wrote:
>>
>>
>>
>> On 7/19/22 09:29, Barry Song wrote:
>>> On Tue, Jul 19, 2022 at 3:35 PM Anshuman Khandual
>>> <anshuman.khandual@xxxxxxx> wrote:
>>>>
>>>>
>>>>
>>>> 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.
>>>
>>> Hi Anshuman, Hi Ying,
>>> Thanks for the comments of both of you. Does the below look ok?
>>>
>>> generic,
>>>
>>> static inline bool arch_wants_thp_swap(void)
>>> {
>>> return IS_ENABLED(CONFIG_THP_SWAP);
>>> }
>>>
>>> arm64,
>>>
>>> static inline bool arch_thp_swp_supported(void)
>>> {
>>> return IS_ENABLED(CONFIG_THP_SWAP) && !system_supports_mte();
>>> }
>>>
>>> caller,
>>>
>>> folio_alloc_swap(struct folio *folio)
>>> {
>>>
>>> if (folio_test_large(folio)) {
>>> - if (IS_ENABLED(CONFIG_THP_SWAP))
>>> + if (arch_thp_swp_supported())
>>> get_swap_pages(1, &entry, folio_nr_pages(folio));
>>> goto out;
>>> }
>>
>> Current proposal in this patch LGTM, I dont see any reason for these changes.
>
> OK, thanks, Anshuman. Can I collect this as a Reviewed-by?
Yes please.
Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
