On Tue, Jul 19, 2022 at 3:59 PM Barry Song <21cnbao@xxxxxxxxx> 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);
> }
>
sorry, i actually meant arch_thp_swp_supported() but not
arch_wants_thp_swap() in generic code,
static inline bool arch_thp_swp_supported(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;
> }
>
> Thanks
> Barry
