Message-ID: <CAGsJ_4wFiQe5BZeLQDjUQNUZzDsTLR5QpHA5g9ZCUVOUFrvXTA@mail.gmail.com>
Date:   Wed, 20 Jul 2022 13:46:06 +1200
From:   Barry Song <21cnbao@...il.com>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     "Huang, Ying" <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        LAK <linux-arm-kernel@...ts.infradead.org>,
        Linux-MM <linux-mm@...ck.org>,
        Steven Price <steven.price@....com>,
        Will Deacon <will@...nel.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        郭健 <guojian@...o.com>,
        hanchuanhua <hanchuanhua@...o.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Hugh Dickins <hughd@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Minchan Kim <minchan@...nel.org>,
        Yang Shi <shy828301@...il.com>,
        Barry Song <v-songbaohua@...o.com>,
        张诗明(Simon Zhang) 
        <zhangshiming@...o.com>
Subject: Re: [RESEND PATCH v3] arm64: enable THP_SWAP for arm64

On Tue, Jul 19, 2022 at 4:04 PM Anshuman Khandual
<anshuman.khandual@....com> wrote:
>
>
>
> On 7/19/22 09:29, Barry Song wrote:
> > On Tue, Jul 19, 2022 at 3:35 PM Anshuman Khandual
> > <anshuman.khandual@....com> wrote:
> >>
> >>
> >>
> >> On 7/19/22 08:58, Huang, Ying wrote:
> >>> Anshuman Khandual <anshuman.khandual@....com> writes:
> >>>
> >>>> On 7/19/22 06:53, Barry Song wrote:
> >>>>> On Tue, Jul 19, 2022 at 12:44 PM Huang, Ying <ying.huang@...el.com> wrote:
> >>>>>>
> >>>>>> Barry Song <21cnbao@...il.com> writes:
> >>>>>>
> >>>>>>> From: Barry Song <v-songbaohua@...o.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@...el.com>
> >>>>>>> Cc: Minchan Kim <minchan@...nel.org>
> >>>>>>> Cc: Johannes Weiner <hannes@...xchg.org>
> >>>>>>> Cc: Hugh Dickins <hughd@...gle.com>
> >>>>>>> Cc: Andrea Arcangeli <aarcange@...hat.com>
> >>>>>>> Cc: Anshuman Khandual <anshuman.khandual@....com>
> >>>>>>> Cc: Steven Price <steven.price@....com>
> >>>>>>> Cc: Yang Shi <shy828301@...il.com>
> >>>>>>> Signed-off-by: Barry Song <v-songbaohua@...o.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);
> >>>>>> }
> >>>>>
> >>>>> 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?

Barry

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