Commit 2bdba986 authored by Ryan Roberts's avatar Ryan Roberts Committed by Andrew Morton
Browse files

mm: thp: batch-collapse PMD with set_ptes() 

Refactor __split_huge_pmd_locked() so that a present PMD can be collapsed
to PTEs in a single batch using set_ptes().

This should improve performance a little bit, but the real motivation is
to remove the need for the arm64 backend to have to fold the contpte
entries.  Instead, since the ptes are set as a batch, the contpte blocks
can be initially set up pre-folded (once the arm64 contpte support is
added in the next few patches).  This leads to noticeable performance
improvement during split.

Link: https://lkml.kernel.org/r/20240215103205.2607016-3-ryan.roberts@arm.com


Signed-off-by: default avatarRyan Roberts <ryan.roberts@arm.com>
Acked-by: default avatarDavid Hildenbrand <david@redhat.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: John Hubbard <jhubbard@nvidia.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>
parent 6280d731

mm/huge_memory.c

+33 −25
Original line number Diff line number Diff line
@@ -2579,15 +2579,16 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, 


	pte = pte_offset_map(&_pmd, haddr);

	VM_BUG_ON(!pte);

	for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {

		pte_t entry;



	/*

		 * Note that NUMA hinting access restrictions are not

		 * transferred to avoid any possibility of altering

		 * permissions across VMAs.

	 * Note that NUMA hinting access restrictions are not transferred to

	 * avoid any possibility of altering permissions across VMAs.

	 */

	if (freeze || pmd_migration) {

		for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {

			pte_t entry;

			swp_entry_t swp_entry;



			if (write)

				swp_entry = make_writable_migration_entry(

							page_to_pfn(page + i));
@@ -2606,8 +2607,14 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, 
				entry = pte_swp_mksoft_dirty(entry);

			if (uffd_wp)

				entry = pte_swp_mkuffd_wp(entry);



			VM_WARN_ON(!pte_none(ptep_get(pte + i)));

			set_pte_at(mm, addr, pte + i, entry);

		}

	} else {

			entry = mk_pte(page + i, READ_ONCE(vma->vm_page_prot));

		pte_t entry;



		entry = mk_pte(page, READ_ONCE(vma->vm_page_prot));

		if (write)

			entry = pte_mkwrite(entry, vma);

		if (!young)
@@ -2619,12 +2626,13 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, 
			entry = pte_mksoft_dirty(entry);

		if (uffd_wp)

			entry = pte_mkuffd_wp(entry);



		for (i = 0; i < HPAGE_PMD_NR; i++)

			VM_WARN_ON(!pte_none(ptep_get(pte + i)));



		set_ptes(mm, haddr, pte, entry, HPAGE_PMD_NR);

	}

		VM_BUG_ON(!pte_none(ptep_get(pte)));

		set_pte_at(mm, addr, pte, entry);

		pte++;

	}

	pte_unmap(pte - 1);

	pte_unmap(pte);



	if (!pmd_migration)

		folio_remove_rmap_pmd(folio, page, vma);