Commit 6db18de4 authored by Ryan Roberts's avatar Ryan Roberts Committed by Kefeng Wang
Browse files

mm: add pte_batch_hint() to reduce scanning in folio_pte_batch() 

mainline inclusion
from mainline-v6.9-rc1
commit c6ec76a2ebc5829e5826b218d2e1475ec11b333e
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I9CUEQ
CVE: NA

-------------------------------------------------

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@arm.com


Signed-off-by: default avatarRyan Roberts <ryan.roberts@arm.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.com>
Tested-by: default avatarJohn Hubbard <jhubbard@nvidia.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Barry Song <21cnbao@gmail.com>
Cc: Borislav Petkov (AMD) <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Morse <james.morse@arm.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
(cherry picked from commit c6ec76a2ebc5829e5826b218d2e1475ec11b333e)
Signed-off-by: default avatarKefeng Wang <wangkefeng.wang@huawei.com>
parent 80b97f4a

include/linux/pgtable.h

+21 −0
Original line number Diff line number Diff line
@@ -205,6 +205,27 @@ static inline int pmd_young(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)

{

mm/memory.c

+12 −7
Original line number Diff line number Diff line
@@ -993,16 +993,20 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, 
{

	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);
@@ -1016,17 +1020,18 @@ static inline int folio_pte_batch(struct folio *folio, unsigned long addr, 
		 * 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);

}



/*