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Mon, 11 May 2026 19:00:07 +0000 (UTC) Received: from p1.redhat.com (unknown [10.44.22.3]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 17C493002D30; Mon, 11 May 2026 18:59:48 +0000 (UTC) From: Nico Pache To: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Cc: aarcange@redhat.com, akpm@linux-foundation.org, anshuman.khandual@arm.com, apopple@nvidia.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, byungchul@sk.com, catalin.marinas@arm.com, cl@gentwo.org, corbet@lwn.net, dave.hansen@linux.intel.com, david@kernel.org, dev.jain@arm.com, gourry@gourry.net, hannes@cmpxchg.org, hughd@google.com, jack@suse.cz, jackmanb@google.com, jannh@google.com, jglisse@google.com, joshua.hahnjy@gmail.com, kas@kernel.org, lance.yang@linux.dev, liam@infradead.org, ljs@kernel.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, mhiramat@kernel.org, mhocko@suse.com, npache@redhat.com, peterx@redhat.com, pfalcato@suse.de, rakie.kim@sk.com, raquini@redhat.com, rdunlap@infradead.org, richard.weiyang@gmail.com, rientjes@google.com, rostedt@goodmis.org, rppt@kernel.org, ryan.roberts@arm.com, shivankg@amd.com, sunnanyong@huawei.com, surenb@google.com, thomas.hellstrom@linux.intel.com, tiwai@suse.de, usamaarif642@gmail.com, vbabka@suse.cz, vishal.moola@gmail.com, wangkefeng.wang@huawei.com, will@kernel.org, willy@infradead.org, yang@os.amperecomputing.com, ying.huang@linux.alibaba.com, ziy@nvidia.com, zokeefe@google.com Subject: [PATCH mm-unstable v17 06/14] mm/khugepaged: generalize collapse_huge_page for mTHP collapse Date: Mon, 11 May 2026 12:58:06 -0600 Message-ID: <20260511185817.686831-7-npache@redhat.com> In-Reply-To: <20260511185817.686831-1-npache@redhat.com> References: <20260511185817.686831-1-npache@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: L-2HSY-4o4JV_VZZuHeJ0z7i61hHxoSdZDJGl8UIQvo_1778526008 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true X-Stat-Signature: inyfegxowsrug83yk3tai3f8uwgwy7q8 X-Rspam-User: X-Rspamd-Queue-Id: 33C7040010 X-Rspamd-Server: rspam07 X-HE-Tag: 1778526019-656295 X-HE-Meta: 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 3AH0c7Er BnVPjw05rPh7psjlyz4DDl/oIbpO7SUPP65fiU9FrXxqnhzoBoxj203VgZdu4cV+ex++a9mjntcOaZgWeZi52YbqUCbnvMeOy0VLkKMV8Y0ZNp5FIsFwo2FQhsy4EQaCBgXs2sc+eQk3kWYo1dZ0GFyMykHJ/Nwrd2k0dt7rEkBXRVnbCH0fRpxhoRm1uk8VwDeN5plSKjmRv+zkTgGidDJ90AcIrHqtrQ8la1gjmib0SurHQJDndGMN6V0MGVkxy0B1K/otZRV513ajZNSXag/ZSFLngonSvtdo0JclFyvoW22zecJ/nWLExRYt1nbI/3ZTyu/BvGtexXvOTMAiAg5jJSELUcBO70i2mBWNY4QQemTUtjO4N6uij692fcglP/l3P19AfCCClrJwz4LDWFMuzQWT+eH2vzrrc54E/EnE6UgMicMuu61kcgge9ZATU2xyGIZWPZjWvlTA= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Pass an order and offset to collapse_huge_page to support collapsing anon memory to arbitrary orders within a PMD. order indicates what mTHP size we are attempting to collapse to, and offset indicates were in the PMD to start the collapse attempt. For non-PMD collapse we must leave the anon VMA write locked until after we collapse the mTHP-- in the PMD case all the pages are isolated, but in the mTHP case this is not true, and we must keep the lock to prevent access/changes to the page tables. This can happen if the rmap walkers hit a pmd_none while the PMD entry is currently unavailable due to being temporarily removed during the collapse phase. Signed-off-by: Nico Pache --- mm/khugepaged.c | 93 +++++++++++++++++++++++++++++-------------------- 1 file changed, 55 insertions(+), 38 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 37a5f6791816..f49bef78cf51 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1207,34 +1207,36 @@ static enum scan_result alloc_charge_folio(struct folio **foliop, struct mm_stru * the mmap_lock during that. We must recheck the vma after taking it again in * write mode. */ -static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long address, - int referenced, int unmapped, struct collapse_control *cc) +static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long start_addr, + int referenced, int unmapped, struct collapse_control *cc, + unsigned int order) { + const unsigned long pmd_addr = start_addr & HPAGE_PMD_MASK; + const unsigned long end_addr = start_addr + (PAGE_SIZE << order); LIST_HEAD(compound_pagelist); pmd_t *pmd, _pmd; - pte_t *pte; + pte_t *pte = NULL; pgtable_t pgtable; struct folio *folio; spinlock_t *pmd_ptl, *pte_ptl; enum scan_result result = SCAN_FAIL; struct vm_area_struct *vma; struct mmu_notifier_range range; + bool anon_vma_locked = false; - VM_BUG_ON(address & ~HPAGE_PMD_MASK); - - result = alloc_charge_folio(&folio, mm, cc, HPAGE_PMD_ORDER); + result = alloc_charge_folio(&folio, mm, cc, order); if (result != SCAN_SUCCEED) goto out_nolock; mmap_read_lock(mm); - result = hugepage_vma_revalidate(mm, address, true, &vma, cc, - HPAGE_PMD_ORDER); + result = hugepage_vma_revalidate(mm, pmd_addr, /*expect_anon=*/ true, + &vma, cc, order); if (result != SCAN_SUCCEED) { mmap_read_unlock(mm); goto out_nolock; } - result = find_pmd_or_thp_or_none(mm, address, &pmd); + result = find_pmd_or_thp_or_none(mm, pmd_addr, &pmd); if (result != SCAN_SUCCEED) { mmap_read_unlock(mm); goto out_nolock; @@ -1246,8 +1248,8 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long a * released when it fails. So we jump out_nolock directly in * that case. Continuing to collapse causes inconsistency. */ - result = __collapse_huge_page_swapin(mm, vma, address, pmd, - referenced, HPAGE_PMD_ORDER); + result = __collapse_huge_page_swapin(mm, vma, start_addr, pmd, + referenced, order); if (result != SCAN_SUCCEED) goto out_nolock; } @@ -1262,20 +1264,21 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long a * mmap_lock. */ mmap_write_lock(mm); - result = hugepage_vma_revalidate(mm, address, true, &vma, cc, - HPAGE_PMD_ORDER); + result = hugepage_vma_revalidate(mm, pmd_addr, /*expect_anon=*/ true, + &vma, cc, order); if (result != SCAN_SUCCEED) goto out_up_write; /* check if the pmd is still valid */ vma_start_write(vma); - result = check_pmd_still_valid(mm, address, pmd); + result = check_pmd_still_valid(mm, pmd_addr, pmd); if (result != SCAN_SUCCEED) goto out_up_write; anon_vma_lock_write(vma->anon_vma); + anon_vma_locked = true; - mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, address, - address + HPAGE_PMD_SIZE); + mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, mm, start_addr, + end_addr); mmu_notifier_invalidate_range_start(&range); pmd_ptl = pmd_lock(mm, pmd); /* probably unnecessary */ @@ -1287,26 +1290,23 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long a * Parallel GUP-fast is fine since GUP-fast will back off when * it detects PMD is changed. */ - _pmd = pmdp_collapse_flush(vma, address, pmd); + _pmd = pmdp_collapse_flush(vma, pmd_addr, pmd); spin_unlock(pmd_ptl); mmu_notifier_invalidate_range_end(&range); tlb_remove_table_sync_one(); - pte = pte_offset_map_lock(mm, &_pmd, address, &pte_ptl); + pte = pte_offset_map_lock(mm, &_pmd, start_addr, &pte_ptl); if (pte) { - result = __collapse_huge_page_isolate(vma, address, pte, cc, - HPAGE_PMD_ORDER, - &compound_pagelist); + result = __collapse_huge_page_isolate(vma, start_addr, pte, cc, + order, &compound_pagelist); spin_unlock(pte_ptl); } else { result = SCAN_NO_PTE_TABLE; } if (unlikely(result != SCAN_SUCCEED)) { - if (pte) - pte_unmap(pte); spin_lock(pmd_ptl); - BUG_ON(!pmd_none(*pmd)); + WARN_ON_ONCE(!pmd_none(*pmd)); /* * We can only use set_pmd_at when establishing * hugepmds and never for establishing regular pmds that @@ -1314,21 +1314,24 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long a */ pmd_populate(mm, pmd, pmd_pgtable(_pmd)); spin_unlock(pmd_ptl); - anon_vma_unlock_write(vma->anon_vma); goto out_up_write; } /* - * All pages are isolated and locked so anon_vma rmap - * can't run anymore. + * For PMD collapse all pages are isolated and locked so anon_vma + * rmap can't run anymore. For mTHP collapse the PMD entry has been + * removed and not all pages are isolated and locked, so we must hold + * the lock to prevent neighboring folios from attempting to access + * this PMD until its reinstalled. */ - anon_vma_unlock_write(vma->anon_vma); + if (is_pmd_order(order)) { + anon_vma_unlock_write(vma->anon_vma); + anon_vma_locked = false; + } result = __collapse_huge_page_copy(pte, folio, pmd, _pmd, - vma, address, pte_ptl, - HPAGE_PMD_ORDER, - &compound_pagelist); - pte_unmap(pte); + vma, start_addr, pte_ptl, + order, &compound_pagelist); if (unlikely(result != SCAN_SUCCEED)) goto out_up_write; @@ -1338,18 +1341,32 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long a * write. */ __folio_mark_uptodate(folio); - pgtable = pmd_pgtable(_pmd); - spin_lock(pmd_ptl); - BUG_ON(!pmd_none(*pmd)); - pgtable_trans_huge_deposit(mm, pmd, pgtable); - map_anon_folio_pmd_nopf(folio, pmd, vma, address); + WARN_ON_ONCE(!pmd_none(*pmd)); + if (is_pmd_order(order)) { + pgtable = pmd_pgtable(_pmd); + pgtable_trans_huge_deposit(mm, pmd, pgtable); + map_anon_folio_pmd_nopf(folio, pmd, vma, pmd_addr); + } else { + /* + * set_ptes is called in map_anon_folio_pte_nopf with the + * pmd_ptl lock still held; this is safe as the PMD is expected + * to be none. The pmd entry is then repopulated below. + */ + map_anon_folio_pte_nopf(folio, pte, vma, start_addr, /*uffd_wp=*/ false); + smp_wmb(); /* make PTEs visible before PMD. See pmd_install() */ + pmd_populate(mm, pmd, pmd_pgtable(_pmd)); + } spin_unlock(pmd_ptl); folio = NULL; result = SCAN_SUCCEED; out_up_write: + if (anon_vma_locked) + anon_vma_unlock_write(vma->anon_vma); + if (pte) + pte_unmap(pte); mmap_write_unlock(mm); out_nolock: if (folio) @@ -1529,7 +1546,7 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, /* collapse_huge_page expects the lock to be dropped before calling */ mmap_read_unlock(mm); result = collapse_huge_page(mm, start_addr, referenced, - unmapped, cc); + unmapped, cc, HPAGE_PMD_ORDER); /* collapse_huge_page will return with the mmap_lock released */ *lock_dropped = true; } -- 2.54.0