From nobody Wed Oct 8 19:05:21 2025 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 385CC15A86B for ; Wed, 25 Jun 2025 05:58:26 +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=1750831108; cv=none; b=JdtJ79xayMK1Nh1jDxG4AsP+om8BkBXAwV/dbwFmbvVOO88EOxBI3KwrjJ2PXLBVJ9CS/Nzpi0QXTnfhqe4B8UvQiww6Cz6IYj8gThHtd3dWLH83GZnD0oszYxIENDqzY0OEkJB+mKOxQLYjii+KZRnxmTtA8U4j+g1XyQw45pE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750831108; c=relaxed/simple; bh=SNSi/uMwV++FgdgG8uEvRDD9DYGOweXb8I1Sbxv7M0o=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=L4vbS+lLoXzth166+eGuAcbShu0QZEXQj7MWfC/sAz4gZGS33rDZUZzkCgNbfmds1u5/Yqfplfug8BSCnHyQou8EvA7qhcdVPadkGkgBZSx30DVMmge8Ng12tYNv5pPvtz79vwD6aWLAKjVjv2Oi35Curf+phCsqGkX1X6T9lkE= 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 6EF671063; Tue, 24 Jun 2025 22:58:08 -0700 (PDT) Received: from MacBook-Pro.blr.arm.com (MacBook-Pro.blr.arm.com [10.164.18.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id BBB743F63F; Tue, 24 Jun 2025 22:58:22 -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 1/3] khugepaged: Optimize __collapse_huge_page_copy_succeeded() by PTE batching Date: Wed, 25 Jun 2025 11:28:04 +0530 Message-Id: <20250625055806.82645-2-dev.jain@arm.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20250625055806.82645-1-dev.jain@arm.com> References: <20250625055806.82645-1-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 optimize __collapse_huge_page_copy_succeeded(). On arm64, suppose khugepaged is scanning a pte-mapped 2MB THP for collapse. Then, calling ptep_clear() for every pte will cause a TLB flush for every contpte block. Instead, clear_full_ptes() does a contpte_try_unfold_partial() which will flush the TLB only for the (if any) starting and ending contpte block, if they partially overlap with the range khugepaged is looking at. For all arches, there should be a benefit due to batching atomic operations on mapcounts due to folio_remove_rmap_ptes(). No issues were observed with mm-selftests. Signed-off-by: Dev Jain --- mm/khugepaged.c | 27 +++++++++++++++++++++------ 1 file changed, 21 insertions(+), 6 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index d45d08b521f6..3944b112d452 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -700,12 +700,15 @@ static void __collapse_huge_page_copy_succeeded(pte_t= *pte, spinlock_t *ptl, struct list_head *compound_pagelist) { + unsigned long end =3D address + HPAGE_PMD_SIZE; struct folio *src, *tmp; - pte_t *_pte; pte_t pteval; + pte_t *_pte; + int nr_ptes; =20 - for (_pte =3D pte; _pte < pte + HPAGE_PMD_NR; - _pte++, address +=3D PAGE_SIZE) { + for (_pte =3D pte; _pte < pte + HPAGE_PMD_NR; _pte +=3D nr_ptes, + address +=3D nr_ptes * PAGE_SIZE) { + nr_ptes =3D 1; pteval =3D ptep_get(_pte); if (pte_none(pteval) || is_zero_pfn(pte_pfn(pteval))) { add_mm_counter(vma->vm_mm, MM_ANONPAGES, 1); @@ -719,21 +722,33 @@ static void __collapse_huge_page_copy_succeeded(pte_t= *pte, ksm_might_unmap_zero_page(vma->vm_mm, pteval); } } else { + const fpb_t flags =3D FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY; + int max_nr_ptes; + struct page *src_page =3D pte_page(pteval); =20 src =3D page_folio(src_page); if (!folio_test_large(src)) release_pte_folio(src); + + max_nr_ptes =3D (end - address) >> PAGE_SHIFT; + if (folio_test_large(src)) + nr_ptes =3D folio_pte_batch(src, address, _pte, + pteval, max_nr_ptes, + flags, NULL, NULL, NULL); + /* * ptl mostly unnecessary, but preempt has to * be disabled to update the per-cpu stats * inside folio_remove_rmap_pte(). */ spin_lock(ptl); - ptep_clear(vma->vm_mm, address, _pte); - folio_remove_rmap_pte(src, src_page, vma); + clear_full_ptes(vma->vm_mm, address, _pte, nr_ptes, + /* full =3D */ false); + folio_remove_rmap_ptes(src, src_page, nr_ptes, vma); spin_unlock(ptl); - free_folio_and_swap_cache(src); + free_swap_cache(src); + folio_put_refs(src, nr_ptes); } } =20 --=20 2.30.2 From nobody Wed Oct 8 19:05:21 2025 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 8713C1DE2D8 for ; Wed, 25 Jun 2025 05:58:31 +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=1750831114; cv=none; b=mHsfcNut2Dgsintg6CUhyrFWoSkAw+vQXqXEaWH1xp11PbAlyQMiDiZanf2Qs4961ugfbkSPS0zjJfLWKbcwpEAy0L50U6nIDIAoG0ZPvgHS/fSmNS/UKriEG9khbxBgMXRuGXRjcOpWWceTmBMHWOzb1iwiEm7MH/4CAwp5zdM= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750831114; c=relaxed/simple; bh=egfCOXByKrWZlhfRfwjHZY6gZ+HFuN29/Y7LH9KNOpU=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=JxaEU+OYpU10d2BWnnF+qHkRBdfQqCovtCy6zBgCiUY/wpGS5riFSLoJ1L7H9f+V/HveEM+gNJ8l4YA573ldqV/ub8ppueT/tz9r5jB2VH52yKoOugQeH4DUCd7yOpVxiS63Ikrf4EHYurYvSr0wQrp9yjeM2a0J1T99EKFOY0o= 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 CBC8F1063; Tue, 24 Jun 2025 22:58:12 -0700 (PDT) Received: from MacBook-Pro.blr.arm.com (MacBook-Pro.blr.arm.com [10.164.18.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 2E88A3F63F; Tue, 24 Jun 2025 22:58:26 -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 v2 2/3] khugepaged: Optimize collapse_pte_mapped_thp() for large folios by PTE batching Date: Wed, 25 Jun 2025 11:28:05 +0530 Message-Id: <20250625055806.82645-3-dev.jain@arm.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20250625055806.82645-1-dev.jain@arm.com> References: <20250625055806.82645-1-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 optimize collapse_pte_mapped_thp(). On arm64, suppose khugepaged is scanning a pte-mapped 2MB THP for collapse. Then, calling ptep_clear() for every pte will cause a TLB flush for every contpte block. Instead, clear_full_ptes() does a contpte_try_unfold_partial() which will flush the TLB only for the (if any) starting and ending contpte block, if they partially overlap with the range khugepaged is looking at. For all arches, there should be a benefit due to batching atomic operations on mapcounts due to folio_remove_rmap_ptes(). 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. No issues were observed with mm-selftests. Signed-off-by: Dev Jain --- mm/khugepaged.c | 38 ++++++++++++++++++++++++++------------ 1 file changed, 26 insertions(+), 12 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 3944b112d452..4c8d33abfbd8 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1499,15 +1499,16 @@ 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, nr_batch_ptes, result =3D SCAN_FAIL; 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); @@ -1621,11 +1622,17 @@ 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) { + const fpb_t flags =3D FPB_IGNORE_DIRTY | FPB_IGNORE_SOFT_DIRTY; + int max_nr_batch_ptes =3D (end - addr) >> PAGE_SHIFT; + struct folio *mapped_folio; struct page *page; pte_t ptent =3D ptep_get(pte); =20 + nr_batch_ptes =3D 1; + if (pte_none(ptent)) continue; /* @@ -1639,26 +1646,33 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, u= nsigned long addr, goto abort; } page =3D vm_normal_page(vma, addr, ptent); + mapped_folio =3D page_folio(page); + if (folio_page(folio, i) !=3D page) goto abort; =20 + mapped_folio =3D page_folio(page); + nr_batch_ptes =3D folio_pte_batch(mapped_folio, addr, pte, ptent, + max_nr_batch_ptes, flags, + NULL, NULL, NULL); + /* * 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_full_ptes(mm, addr, pte, nr_batch_ptes, /* full =3D */ false); + 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 */ @@ -1691,10 +1705,10 @@ 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 From nobody Wed Oct 8 19:05:21 2025 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id EE87D1DE2D8 for ; Wed, 25 Jun 2025 05:58:35 +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=1750831117; cv=none; b=L4B92kbrX/5KU49NPLm4UxsYuij3ul9WwU/qJ5l3NyZu289S1BOdPdX3UyMSBj4YYRkI3XqSbqRCMquHhBIxOGiFSg7J/SGJsG7bqwPIKukjVmy9WoivxIK9okpcFJVb/rylckWPdpQUdcEQgSaQ2PjcxQ9CNmCI0r6LoLYar9Y= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750831117; c=relaxed/simple; bh=vCme5Rj/mZVPR5MwtxDjtv6Ggu3YPOsadkwygQVt+II=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=iqbiNzylfqqCD+9WU7Mdi9Pb6xe05Fcz5bD6O0zhKF9XSsuNBDyTigwuKRpd9OF4x47jpb1LyJIGHIp5Z792e3HsK6/OOBTJIAg8RbUaZBXehiK11uR3VA3JSR2UkhVzsqMhXM9woIFfncCi7NcqAfG13b+baCDQqj6ia6AXwLA= 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 356961063; Tue, 24 Jun 2025 22:58:17 -0700 (PDT) Received: from MacBook-Pro.blr.arm.com (MacBook-Pro.blr.arm.com [10.164.18.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 8C1093F63F; Tue, 24 Jun 2025 22:58:31 -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 v2 3/3] khugepaged: Reduce race probability between migration and khugepaged Date: Wed, 25 Jun 2025 11:28:06 +0530 Message-Id: <20250625055806.82645-4-dev.jain@arm.com> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: <20250625055806.82645-1-dev.jain@arm.com> References: <20250625055806.82645-1-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" Suppose a folio is under migration, and khugepaged is also trying to collapse it. collapse_pte_mapped_thp() will retrieve the folio from the page cache via filemap_lock_folio(), thus taking a reference on the folio and sleeping on the folio lock, since the lock is held by the migration path. Migration will then fail in __folio_migrate_mapping -> folio_ref_freeze. Reduce the probability of such a race happening (leading to migration failure) by bailing out if we detect a PMD is marked with a migration entry. This fixes the migration-shared-anon-thp testcase failure on Apple M3. Signed-off-by: Dev Jain --- mm/khugepaged.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 4c8d33abfbd8..bc8774f62e86 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -31,6 +31,7 @@ enum scan_result { SCAN_FAIL, SCAN_SUCCEED, SCAN_PMD_NULL, + SCAN_PMD_MIGRATION, SCAN_PMD_NONE, SCAN_PMD_MAPPED, SCAN_EXCEED_NONE_PTE, @@ -956,6 +957,8 @@ static inline int check_pmd_state(pmd_t *pmd) =20 if (pmd_none(pmde)) return SCAN_PMD_NONE; + if (is_pmd_migration_entry(pmde)) + return SCAN_PMD_MIGRATION; if (!pmd_present(pmde)) return SCAN_PMD_NULL; if (pmd_trans_huge(pmde)) @@ -1518,9 +1521,12 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, un= signed long addr, !range_in_vma(vma, haddr, haddr + HPAGE_PMD_SIZE)) return SCAN_VMA_CHECK; =20 - /* Fast check before locking page if already PMD-mapped */ + /* + * Fast check before locking folio if already PMD-mapped, or if the + * folio is under migration + */ result =3D find_pmd_or_thp_or_none(mm, haddr, &pmd); - if (result =3D=3D SCAN_PMD_MAPPED) + if (result =3D=3D SCAN_PMD_MAPPED || result =3D=3D SCAN_PMD_MIGRATION) return result; =20 /* @@ -2745,6 +2751,7 @@ static int madvise_collapse_errno(enum scan_result r) case SCAN_PAGE_LRU: case SCAN_DEL_PAGE_LRU: case SCAN_PAGE_FILLED: + case SCAN_PMD_MIGRATION: return -EAGAIN; /* * Other: Trying again likely not to succeed / error intrinsic to @@ -2834,6 +2841,7 @@ int madvise_collapse(struct vm_area_struct *vma, stru= ct vm_area_struct **prev, goto handle_result; /* Whitelisted set of results where continuing OK */ case SCAN_PMD_NULL: + case SCAN_PMD_MIGRATION: case SCAN_PTE_NON_PRESENT: case SCAN_PTE_UFFD_WP: case SCAN_PAGE_RO: --=20 2.30.2