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;
+}
+#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;
}
--
2.25.1
