From nobody Mon Oct 6 08:28:01 2025 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id C8D231F5858 for ; Thu, 24 Jul 2025 05:23:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753334605; cv=none; b=nG8CBwL0acSrb6nbhFyMAuGbIQ39NV3l8Xz0dCbyQvi57DFQ55nl+6NlcVdGEDauhwvwnm9ulDK7e6304ELHhXgWIuVpQ1LyPBsHOBmlfTovN7egt8HW9u4wUgBVfWcwpKDSb0Yw4PkPWKut26FV3ReaiVqCDPwD0rBEnArOkmQ= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753334605; c=relaxed/simple; bh=dQNdODB7MyOXZDwY7hOhj6RuDPpoZVtEOGPfSbKamw8=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=bbSPtZvYlNOLmE/Una1MN0eYB0llPXM2IXK2yFn4mDH8G/pU8wWwy4/sEhzsvIXKpc8pQnoDA3cvxvqmOCTX3DrfGq5Lp4NWTpeCZ3qEqW/NDjAKIn2ODzHNOkVfp2uPrLbVujGmGbEIwJlWsZ32l527r8yuZGSWWfvlS6jDKlE= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id B86AF1A32; Wed, 23 Jul 2025 22:23:16 -0700 (PDT) Received: from MacBook-Pro.blr.arm.com (unknown [10.164.18.48]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 5B6FB3F66E; Wed, 23 Jul 2025 22:23:19 -0700 (PDT) From: Dev Jain To: akpm@linux-foundation.org, david@redhat.com Cc: ziy@nvidia.com, baolin.wang@linux.alibaba.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, baohua@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dev Jain Subject: [PATCH v4 3/3] khugepaged: Optimize collapse_pte_mapped_thp() by PTE batching Date: Thu, 24 Jul 2025 10:53:01 +0530 Message-Id: <20250724052301.23844-4-dev.jain@arm.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20250724052301.23844-1-dev.jain@arm.com> References: <20250724052301.23844-1-dev.jain@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Use PTE batching to batch process PTEs mapping the same large folio. An improvement is expected due to batching mapcount manipulation on the folios, and for arm64 which supports contig mappings, the number of TLB flushes is also reduced. Note that we do not need to make a change to the check "if (folio_page(folio, i) !=3D page)"; if i'th page of the folio is equal to the first page of our batch, then i + 1, .... i + nr_batch_ptes - 1 pages of the folio will be equal to the corresponding pages of our batch mapping consecutive pages. Acked-by: David Hildenbrand Reviewed-by: Baolin Wang Signed-off-by: Dev Jain Reviewed-by: Lorenzo Stoakes Reviewed-by: Zi Yan --- mm/khugepaged.c | 33 +++++++++++++++++++++------------ 1 file changed, 21 insertions(+), 12 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index f23e943506bc..374a6a5193a7 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1503,15 +1503,17 @@ static int set_huge_pmd(struct vm_area_struct *vma,= unsigned long addr, int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr, bool install_pmd) { + int nr_mapped_ptes =3D 0, result =3D SCAN_FAIL; + unsigned int nr_batch_ptes; struct mmu_notifier_range range; bool notified =3D false; unsigned long haddr =3D addr & HPAGE_PMD_MASK; + unsigned long end =3D haddr + HPAGE_PMD_SIZE; struct vm_area_struct *vma =3D vma_lookup(mm, haddr); struct folio *folio; pte_t *start_pte, *pte; pmd_t *pmd, pgt_pmd; spinlock_t *pml =3D NULL, *ptl; - int nr_ptes =3D 0, result =3D SCAN_FAIL; int i; =20 mmap_assert_locked(mm); @@ -1625,11 +1627,15 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, u= nsigned long addr, goto abort; =20 /* step 2: clear page table and adjust rmap */ - for (i =3D 0, addr =3D haddr, pte =3D start_pte; - i < HPAGE_PMD_NR; i++, addr +=3D PAGE_SIZE, pte++) { + for (i =3D 0, addr =3D haddr, pte =3D start_pte; i < HPAGE_PMD_NR; + i +=3D nr_batch_ptes, addr +=3D nr_batch_ptes * PAGE_SIZE, + pte +=3D nr_batch_ptes) { + unsigned int max_nr_batch_ptes =3D (end - addr) >> PAGE_SHIFT; struct page *page; pte_t ptent =3D ptep_get(pte); =20 + nr_batch_ptes =3D 1; + if (pte_none(ptent)) continue; /* @@ -1643,26 +1649,29 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, u= nsigned long addr, goto abort; } page =3D vm_normal_page(vma, addr, ptent); + if (folio_page(folio, i) !=3D page) goto abort; =20 + nr_batch_ptes =3D folio_pte_batch(folio, pte, ptent, max_nr_batch_ptes); + /* * Must clear entry, or a racing truncate may re-remove it. * TLB flush can be left until pmdp_collapse_flush() does it. * PTE dirty? Shmem page is already dirty; file is read-only. */ - ptep_clear(mm, addr, pte); - folio_remove_rmap_pte(folio, page, vma); - nr_ptes++; + clear_ptes(mm, addr, pte, nr_batch_ptes); + folio_remove_rmap_ptes(folio, page, nr_batch_ptes, vma); + nr_mapped_ptes +=3D nr_batch_ptes; } =20 if (!pml) spin_unlock(ptl); =20 /* step 3: set proper refcount and mm_counters. */ - if (nr_ptes) { - folio_ref_sub(folio, nr_ptes); - add_mm_counter(mm, mm_counter_file(folio), -nr_ptes); + if (nr_mapped_ptes) { + folio_ref_sub(folio, nr_mapped_ptes); + add_mm_counter(mm, mm_counter_file(folio), -nr_mapped_ptes); } =20 /* step 4: remove empty page table */ @@ -1695,10 +1704,10 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, u= nsigned long addr, : SCAN_SUCCEED; goto drop_folio; abort: - if (nr_ptes) { + if (nr_mapped_ptes) { flush_tlb_mm(mm); - folio_ref_sub(folio, nr_ptes); - add_mm_counter(mm, mm_counter_file(folio), -nr_ptes); + folio_ref_sub(folio, nr_mapped_ptes); + add_mm_counter(mm, mm_counter_file(folio), -nr_mapped_ptes); } unlock: if (start_pte) --=20 2.30.2