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.
That will confuse people too.
And the "redundant" checking has no run time overhead, because compiler
will do the trick.
Best Regards,
Huang, Ying
>>>
>>> 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;
>>>> }
>>
>> Thanks
>> Barry
>>
