The quilt patch titled
Subject: mm: add pte_batch_hint() to reduce scanning in folio_pte_batch()
has been removed from the -mm tree. Its filename was
mm-add-pte_batch_hint-to-reduce-scanning-in-folio_pte_batch.patch
This patch was dropped because it was merged into the mm-stable branch
of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
------------------------------------------------------
From: Ryan Roberts <ryan.roberts@xxxxxxx>
Subject: mm: add pte_batch_hint() to reduce scanning in folio_pte_batch()
Date: Thu, 15 Feb 2024 10:32:02 +0000
Some architectures (e.g. arm64) can tell from looking at a pte, if some
follow-on ptes also map contiguous physical memory with the same pgprot.
(for arm64, these are contpte mappings).
Take advantage of this knowledge to optimize folio_pte_batch() so that it
can skip these ptes when scanning to create a batch. By default, if an
arch does not opt-in, folio_pte_batch() returns a compile-time 1, so the
changes are optimized out and the behaviour is as before.
arm64 will opt-in to providing this hint in the next patch, which will
greatly reduce the cost of ptep_get() when scanning a range of contptes.
Link: https://lkml.kernel.org/r/20240215103205.2607016-16-ryan.roberts@xxxxxxx
Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx>
Acked-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: Mark Rutland <mark.rutland@xxxxxxx>
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>
---
include/linux/pgtable.h | 21 +++++++++++++++++++++
mm/memory.c | 19 ++++++++++++-------
2 files changed, 33 insertions(+), 7 deletions(-)
--- a/include/linux/pgtable.h~mm-add-pte_batch_hint-to-reduce-scanning-in-folio_pte_batch
+++ a/include/linux/pgtable.h
@@ -212,6 +212,27 @@ static inline int pmd_dirty(pmd_t pmd)
#define arch_flush_lazy_mmu_mode() do {} while (0)
#endif
+#ifndef pte_batch_hint
+/**
+ * pte_batch_hint - Number of pages that can be added to batch without scanning.
+ * @ptep: Page table pointer for the entry.
+ * @pte: Page table entry.
+ *
+ * Some architectures know that a set of contiguous ptes all map the same
+ * contiguous memory with the same permissions. In this case, it can provide a
+ * hint to aid pte batching without the core code needing to scan every pte.
+ *
+ * An architecture implementation may ignore the PTE accessed state. Further,
+ * the dirty state must apply atomically to all the PTEs described by the hint.
+ *
+ * May be overridden by the architecture, else pte_batch_hint is always 1.
+ */
+static inline unsigned int pte_batch_hint(pte_t *ptep, pte_t pte)
+{
+ return 1;
+}
+#endif
+
#ifndef pte_advance_pfn
static inline pte_t pte_advance_pfn(pte_t pte, unsigned long nr)
{
--- a/mm/memory.c~mm-add-pte_batch_hint-to-reduce-scanning-in-folio_pte_batch
+++ a/mm/memory.c
@@ -988,16 +988,20 @@ static inline int folio_pte_batch(struct
{
unsigned long folio_end_pfn = folio_pfn(folio) + folio_nr_pages(folio);
const pte_t *end_ptep = start_ptep + max_nr;
- pte_t expected_pte = __pte_batch_clear_ignored(pte_next_pfn(pte), flags);
- pte_t *ptep = start_ptep + 1;
+ pte_t expected_pte, *ptep;
bool writable;
+ int nr;
if (any_writable)
*any_writable = false;
VM_WARN_ON_FOLIO(!pte_present(pte), folio);
- while (ptep != end_ptep) {
+ nr = pte_batch_hint(start_ptep, pte);
+ expected_pte = __pte_batch_clear_ignored(pte_advance_pfn(pte, nr), flags);
+ ptep = start_ptep + nr;
+
+ while (ptep < end_ptep) {
pte = ptep_get(ptep);
if (any_writable)
writable = !!pte_write(pte);
@@ -1011,17 +1015,18 @@ static inline int folio_pte_batch(struct
* corner cases the next PFN might fall into a different
* folio.
*/
- if (pte_pfn(pte) == folio_end_pfn)
+ if (pte_pfn(pte) >= folio_end_pfn)
break;
if (any_writable)
*any_writable |= writable;
- expected_pte = pte_next_pfn(expected_pte);
- ptep++;
+ nr = pte_batch_hint(ptep, pte);
+ expected_pte = pte_advance_pfn(expected_pte, nr);
+ ptep += nr;
}
- return ptep - start_ptep;
+ return min(ptep - start_ptep, max_nr);
}
/*
_
Patches currently in -mm which might be from ryan.roberts@xxxxxxx are
