The patch titled
Subject: arm64/mm: implement pte_batch_hint()
has been added to the -mm mm-unstable branch. Its filename is
arm64-mm-implement-pte_batch_hint.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/arm64-mm-implement-pte_batch_hint.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Ryan Roberts <ryan.roberts@xxxxxxx>
Subject: arm64/mm: implement pte_batch_hint()
Date: Thu, 15 Feb 2024 10:32:03 +0000
When core code iterates over a range of ptes and calls ptep_get() for each
of them, if the range happens to cover contpte mappings, the number of pte
reads becomes amplified by a factor of the number of PTEs in a contpte
block. This is because for each call to ptep_get(), the implementation
must read all of the ptes in the contpte block to which it belongs to
gather the access and dirty bits.
This causes a hotspot for fork(), as well as operations that unmap memory
such as munmap(), exit and madvise(MADV_DONTNEED). Fortunately we can fix
this by implementing pte_batch_hint() which allows their iterators to skip
getting the contpte tail ptes when gathering the batch of ptes to operate
on. This results in the number of PTE reads returning to 1 per pte.
Link: https://lkml.kernel.org/r/20240215103205.2607016-17-ryan.roberts@xxxxxxx
Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
Tested-by: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
Cc: Barry Song <21cnbao@xxxxxxxxx>
Cc: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: James Morse <james.morse@xxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Marc Zyngier <maz@xxxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Will Deacon <will@xxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/arm64/include/asm/pgtable.h | 9 +++++++++
1 file changed, 9 insertions(+)
--- a/arch/arm64/include/asm/pgtable.h~arm64-mm-implement-pte_batch_hint
+++ a/arch/arm64/include/asm/pgtable.h
@@ -1213,6 +1213,15 @@ static inline void contpte_try_unfold(st
__contpte_try_unfold(mm, addr, ptep, pte);
}
+#define pte_batch_hint pte_batch_hint
+static inline unsigned int pte_batch_hint(pte_t *ptep, pte_t pte)
+{
+ if (!pte_valid_cont(pte))
+ return 1;
+
+ return CONT_PTES - (((unsigned long)ptep >> 3) & (CONT_PTES - 1));
+}
+
/*
* The below functions constitute the public API that arm64 presents to the
* core-mm to manipulate PTE entries within their page tables (or at least this
_
Patches currently in -mm which might be from ryan.roberts@xxxxxxx are
tools-mm-add-thpmaps-script-to-dump-thp-usage-info.patch
arm64-mm-make-set_ptes-robust-when-oas-cross-48-bit-boundary.patch
mm-clarify-the-spec-for-set_ptes.patch
mm-thp-batch-collapse-pmd-with-set_ptes.patch
mm-introduce-pte_advance_pfn-and-use-for-pte_next_pfn.patch
arm64-mm-convert-pte_next_pfn-to-pte_advance_pfn.patch
x86-mm-convert-pte_next_pfn-to-pte_advance_pfn.patch
mm-tidy-up-pte_next_pfn-definition.patch
arm64-mm-convert-read_onceptep-to-ptep_getptep.patch
arm64-mm-convert-set_pte_at-to-set_ptes-1.patch
arm64-mm-convert-ptep_clear-to-ptep_get_and_clear.patch
arm64-mm-new-ptep-layer-to-manage-contig-bit.patch
arm64-mm-split-__flush_tlb_range-to-elide-trailing-dsb.patch
arm64-mm-wire-up-pte_cont-for-user-mappings.patch
arm64-mm-implement-new-wrprotect_ptes-batch-api.patch
arm64-mm-implement-new-clear_full_ptes-batch-apis.patch
mm-add-pte_batch_hint-to-reduce-scanning-in-folio_pte_batch.patch
arm64-mm-implement-pte_batch_hint.patch
arm64-mm-__always_inline-to-improve-fork-perf.patch
arm64-mm-automatically-fold-contpte-mappings.patch
