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Thu, 22 Jan 2026 19:31:03 +0000 (UTC) Received: from h1.redhat.com (unknown [10.22.88.59]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id D1ED81958DC1; Thu, 22 Jan 2026 19:30:53 +0000 (UTC) From: Nico Pache To: linux-mm@kvack.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org Cc: npache@redhat.com, akpm@linux-foundation.org, david@kernel.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, corbet@lwn.net, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, jannh@google.com, pfalcato@suse.de, jackmanb@google.com, hannes@cmpxchg.org, willy@infradead.org, peterx@redhat.com, wangkefeng.wang@huawei.com, usamaarif642@gmail.com, sunnanyong@huawei.com, vishal.moola@gmail.com, thomas.hellstrom@linux.intel.com, yang@os.amperecomputing.com, kas@kernel.org, aarcange@redhat.com, raquini@redhat.com, anshuman.khandual@arm.com, catalin.marinas@arm.com, tiwai@suse.de, will@kernel.org, dave.hansen@linux.intel.com, jack@suse.cz, cl@gentwo.org, jglisse@google.com, zokeefe@google.com, rientjes@google.com, rdunlap@infradead.org, hughd@google.com, richard.weiyang@gmail.com, David Hildenbrand Subject: [PATCH mm-unstable v14 06/16] khugepaged: generalize __collapse_huge_page_* for mTHP support Date: Thu, 22 Jan 2026 12:28:31 -0700 Message-ID: <20260122192841.128719-7-npache@redhat.com> In-Reply-To: <20260122192841.128719-1-npache@redhat.com> References: <20260122192841.128719-1-npache@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: MLkdiQ_kIaI-bhlRitvwv08C8e4altqtPvo1lGW8MjY_1769110263 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: 8bit content-type: text/plain; charset="US-ASCII"; x-default=true X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 5FB6640004 X-Stat-Signature: d4emmczyiaxctr5p1s3uk7btzxhgp7mk X-HE-Tag: 1769110271-731324 X-HE-Meta: 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 URqq4Jm5 MHE8Zzn36/ye4So5r2fWwggFQ7cC19icfeNy04qgls0zZroRp3rqR5zNyAReVivJ1jn9yx5n6/FaaPddO3jxraAG45x+tTRTeo75EvrW6CX5BRY8M7xW47cl2hmI9BcwwqhFQzRviubQnsQZgn1vYBc/c3nOyoI/5RT8NpoKWSNMfdfyeKCBfy5afwiwERpa6VMFopUBsvZNckp3xWwEHeb1gdTA4wRdLedFQeQ6UXHHait+hcWUt62oRJ1epTEgh3RRu3iBgrySoXKmYE2hjwP4Gvy3LyMkBe5yYKSA2x9OaQ5uLtEqMo0CA3jSv4aZxkm/g0BDj0UJxreV2HUp1qOHlURKieuKg7rDE+OfJrHGj4YOPFjQGqV0/T1njeS++xJBaCCy49/HGUuJcv6vjiudB5dEVFpRvil6hbunqKewGYm7SkPCgGV2pde3E7wPcMTeRgog4kbalTNqN8dIPw/+WkEnbT8lI7H9Kg1S5CQvxsutFk+K5W2bU1hijQbEFHqiHWaden3wHOfEvP2KgZ7iF4ZT6iw+8nUbBIybNeVhAQ18= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: generalize the order of the __collapse_huge_page_* functions to support future mTHP collapse. mTHP collapse will not honor the khugepaged_max_ptes_shared or khugepaged_max_ptes_swap parameters, and will fail if it encounters a shared or swapped entry. No functional changes in this patch. Reviewed-by: Wei Yang Reviewed-by: Lance Yang Reviewed-by: Lorenzo Stoakes Reviewed-by: Baolin Wang Acked-by: David Hildenbrand Co-developed-by: Dev Jain Signed-off-by: Dev Jain Signed-off-by: Nico Pache --- mm/khugepaged.c | 73 +++++++++++++++++++++++++++++++------------------ 1 file changed, 47 insertions(+), 26 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 384d30b6bdd3..0f68902edd9a 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -539,7 +539,7 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte, static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma, unsigned long start_addr, pte_t *pte, struct collapse_control *cc, - struct list_head *compound_pagelist) + unsigned int order, struct list_head *compound_pagelist) { struct page *page = NULL; struct folio *folio = NULL; @@ -547,15 +547,17 @@ static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma, pte_t *_pte; int none_or_zero = 0, shared = 0, referenced = 0; enum scan_result result = SCAN_FAIL; + const unsigned long nr_pages = 1UL << order; + int max_ptes_none = khugepaged_max_ptes_none >> (HPAGE_PMD_ORDER - order); - for (_pte = pte; _pte < pte + HPAGE_PMD_NR; + for (_pte = pte; _pte < pte + nr_pages; _pte++, addr += PAGE_SIZE) { pte_t pteval = ptep_get(_pte); if (pte_none_or_zero(pteval)) { ++none_or_zero; if (!userfaultfd_armed(vma) && (!cc->is_khugepaged || - none_or_zero <= khugepaged_max_ptes_none)) { + none_or_zero <= max_ptes_none)) { continue; } else { result = SCAN_EXCEED_NONE_PTE; @@ -583,8 +585,14 @@ static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma, /* See collapse_scan_pmd(). */ if (folio_maybe_mapped_shared(folio)) { ++shared; - if (cc->is_khugepaged && - shared > khugepaged_max_ptes_shared) { + /* + * TODO: Support shared pages without leading to further + * mTHP collapses. Currently bringing in new pages via + * shared may cause a future higher order collapse on a + * rescan of the same range. + */ + if (!is_pmd_order(order) || (cc->is_khugepaged && + shared > khugepaged_max_ptes_shared)) { result = SCAN_EXCEED_SHARED_PTE; count_vm_event(THP_SCAN_EXCEED_SHARED_PTE); goto out; @@ -677,18 +685,18 @@ static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma, } static void __collapse_huge_page_copy_succeeded(pte_t *pte, - struct vm_area_struct *vma, - unsigned long address, - spinlock_t *ptl, - struct list_head *compound_pagelist) + struct vm_area_struct *vma, unsigned long address, + spinlock_t *ptl, unsigned int order, + struct list_head *compound_pagelist) { - unsigned long end = address + HPAGE_PMD_SIZE; + unsigned long end = address + (PAGE_SIZE << order); struct folio *src, *tmp; pte_t pteval; pte_t *_pte; unsigned int nr_ptes; + const unsigned long nr_pages = 1UL << order; - for (_pte = pte; _pte < pte + HPAGE_PMD_NR; _pte += nr_ptes, + for (_pte = pte; _pte < pte + nr_pages; _pte += nr_ptes, address += nr_ptes * PAGE_SIZE) { nr_ptes = 1; pteval = ptep_get(_pte); @@ -741,13 +749,11 @@ static void __collapse_huge_page_copy_succeeded(pte_t *pte, } static void __collapse_huge_page_copy_failed(pte_t *pte, - pmd_t *pmd, - pmd_t orig_pmd, - struct vm_area_struct *vma, - struct list_head *compound_pagelist) + pmd_t *pmd, pmd_t orig_pmd, struct vm_area_struct *vma, + unsigned int order, struct list_head *compound_pagelist) { spinlock_t *pmd_ptl; - + const unsigned long nr_pages = 1UL << order; /* * Re-establish the PMD to point to the original page table * entry. Restoring PMD needs to be done prior to releasing @@ -761,7 +767,7 @@ static void __collapse_huge_page_copy_failed(pte_t *pte, * Release both raw and compound pages isolated * in __collapse_huge_page_isolate. */ - release_pte_pages(pte, pte + HPAGE_PMD_NR, compound_pagelist); + release_pte_pages(pte, pte + nr_pages, compound_pagelist); } /* @@ -781,16 +787,16 @@ static void __collapse_huge_page_copy_failed(pte_t *pte, */ static enum scan_result __collapse_huge_page_copy(pte_t *pte, struct folio *folio, pmd_t *pmd, pmd_t orig_pmd, struct vm_area_struct *vma, - unsigned long address, spinlock_t *ptl, + unsigned long address, spinlock_t *ptl, unsigned int order, struct list_head *compound_pagelist) { unsigned int i; enum scan_result result = SCAN_SUCCEED; - + const unsigned long nr_pages = 1UL << order; /* * Copying pages' contents is subject to memory poison at any iteration. */ - for (i = 0; i < HPAGE_PMD_NR; i++) { + for (i = 0; i < nr_pages; i++) { pte_t pteval = ptep_get(pte + i); struct page *page = folio_page(folio, i); unsigned long src_addr = address + i * PAGE_SIZE; @@ -809,10 +815,10 @@ static enum scan_result __collapse_huge_page_copy(pte_t *pte, struct folio *foli if (likely(result == SCAN_SUCCEED)) __collapse_huge_page_copy_succeeded(pte, vma, address, ptl, - compound_pagelist); + order, compound_pagelist); else __collapse_huge_page_copy_failed(pte, pmd, orig_pmd, vma, - compound_pagelist); + order, compound_pagelist); return result; } @@ -983,12 +989,12 @@ static enum scan_result check_pmd_still_valid(struct mm_struct *mm, * Returns result: if not SCAN_SUCCEED, mmap_lock has been released. */ static enum scan_result __collapse_huge_page_swapin(struct mm_struct *mm, - struct vm_area_struct *vma, unsigned long start_addr, pmd_t *pmd, - int referenced) + struct vm_area_struct *vma, unsigned long start_addr, + pmd_t *pmd, int referenced, unsigned int order) { int swapped_in = 0; vm_fault_t ret = 0; - unsigned long addr, end = start_addr + (HPAGE_PMD_NR * PAGE_SIZE); + unsigned long addr, end = start_addr + (PAGE_SIZE << order); enum scan_result result; pte_t *pte = NULL; spinlock_t *ptl; @@ -1020,6 +1026,19 @@ static enum scan_result __collapse_huge_page_swapin(struct mm_struct *mm, pte_present(vmf.orig_pte)) continue; + /* + * TODO: Support swapin without leading to further mTHP + * collapses. Currently bringing in new pages via swapin may + * cause a future higher order collapse on a rescan of the same + * range. + */ + if (!is_pmd_order(order)) { + pte_unmap(pte); + mmap_read_unlock(mm); + result = SCAN_EXCEED_SWAP_PTE; + goto out; + } + vmf.pte = pte; vmf.ptl = ptl; ret = do_swap_page(&vmf); @@ -1139,7 +1158,7 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long a * that case. Continuing to collapse causes inconsistency. */ result = __collapse_huge_page_swapin(mm, vma, address, pmd, - referenced); + referenced, HPAGE_PMD_ORDER); if (result != SCAN_SUCCEED) goto out_nolock; } @@ -1187,6 +1206,7 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long a pte = pte_offset_map_lock(mm, &_pmd, address, &pte_ptl); if (pte) { result = __collapse_huge_page_isolate(vma, address, pte, cc, + HPAGE_PMD_ORDER, &compound_pagelist); spin_unlock(pte_ptl); } else { @@ -1217,6 +1237,7 @@ static enum scan_result collapse_huge_page(struct mm_struct *mm, unsigned long a result = __collapse_huge_page_copy(pte, folio, pmd, _pmd, vma, address, pte_ptl, + HPAGE_PMD_ORDER, &compound_pagelist); pte_unmap(pte); if (unlikely(result != SCAN_SUCCEED)) -- 2.52.0