From nobody Mon Apr 6 10:42:07 2026 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D910C284B29 for ; Thu, 26 Feb 2026 03:24:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772076247; cv=none; b=OwdmHFr8v5IHzTpWu1el4GVmSgmaSAGp8CyAqsWCzTklR06JOeh8jacM1vLf20eXonnzpeNYyzPD8VYmUBvPyemtCBO9qJx6qhPAAHFB8OO2k9/XJ3+ZpPhnpIjNV4qnx+Bjx80jIFWJpEuHGYcyjZ8IN5mUaJEIHbNbF1kjacE= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772076247; c=relaxed/simple; bh=/rzBuBuDuTrKhZuqViRSh6onupYckg3An6Z+oC9CV68=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=DiC9qiH29/aJkbfro4PlZeyuymxsYElTrR2v5N50OjDIeW8IUYaSV/s411WC0jWVWDtdapQ8//Pd+jhMBR4/T2sO2P5L7IkGG6mBtYzJ59ymy3LIC92kbhyPi7VQBE5uOsZ2kZWu4x9S8KeBX+Uq/8hUP+NuT+bP+CIEW+/QkWY= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=P2gkLU4x; arc=none smtp.client-ip=170.10.133.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="P2gkLU4x" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1772076243; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=HMaDPMdSo1wOJupzMtNfLzVgCQkuS95wkaCrSiv4DDs=; b=P2gkLU4x2E1YSxr/mfD8iSbsE9f+/OVnTI2IuHg1oSHn9KbB/VlCWCDfqb160y0HEGhabz F6DcEW5i72IGCeBw86LL1zNRux97ZL/PiMSuRWTbDZAxy9937/syYVRdTpbCdEjKQAGCF0 NlpNsltQVUMrCyAeUYrVruPu3V8C92M= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-444-IXPDXZKzM9uiQ3kQ9QqKGw-1; Wed, 25 Feb 2026 22:24:00 -0500 X-MC-Unique: IXPDXZKzM9uiQ3kQ9QqKGw-1 X-Mimecast-MFC-AGG-ID: IXPDXZKzM9uiQ3kQ9QqKGw_1772076239 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 565BD1956058; Thu, 26 Feb 2026 03:23:59 +0000 (UTC) Received: from h1.redhat.com (unknown [10.22.64.173]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 3B8D83003D88; Thu, 26 Feb 2026 03:23:49 +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.Howlett@oracle.com, lorenzo.stoakes@oracle.com, 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 v15 03/13] mm/khugepaged: generalize __collapse_huge_page_* for mTHP support Date: Wed, 25 Feb 2026 20:23:47 -0700 Message-ID: <20260226032347.232939-1-npache@redhat.com> In-Reply-To: <20260226031741.230674-1-npache@redhat.com> References: <20260226031741.230674-1-npache@redhat.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 X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Content-Type: text/plain; charset="utf-8" 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 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 a9b645402b7f..ecdbbf6a01a6 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -535,7 +535,7 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte, =20 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 =3D NULL; struct folio *folio =3D NULL; @@ -543,15 +543,17 @@ static enum scan_result __collapse_huge_page_isolate(= struct vm_area_struct *vma, pte_t *_pte; int none_or_zero =3D 0, shared =3D 0, referenced =3D 0; enum scan_result result =3D SCAN_FAIL; + const unsigned long nr_pages =3D 1UL << order; + int max_ptes_none =3D khugepaged_max_ptes_none >> (HPAGE_PMD_ORDER - orde= r); =20 - for (_pte =3D pte; _pte < pte + HPAGE_PMD_NR; + for (_pte =3D pte; _pte < pte + nr_pages; _pte++, addr +=3D PAGE_SIZE) { pte_t pteval =3D ptep_get(_pte); if (pte_none_or_zero(pteval)) { ++none_or_zero; if (!userfaultfd_armed(vma) && (!cc->is_khugepaged || - none_or_zero <=3D khugepaged_max_ptes_none)) { + none_or_zero <=3D max_ptes_none)) { continue; } else { result =3D SCAN_EXCEED_NONE_PTE; @@ -585,8 +587,14 @@ static enum scan_result __collapse_huge_page_isolate(s= truct 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 =3D SCAN_EXCEED_SHARED_PTE; count_vm_event(THP_SCAN_EXCEED_SHARED_PTE); goto out; @@ -679,18 +687,18 @@ static enum scan_result __collapse_huge_page_isolate(= struct vm_area_struct *vma, } =20 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 =3D address + HPAGE_PMD_SIZE; + unsigned long end =3D address + (PAGE_SIZE << order); struct folio *src, *tmp; pte_t pteval; pte_t *_pte; unsigned int nr_ptes; + const unsigned long nr_pages =3D 1UL << order; =20 - for (_pte =3D pte; _pte < pte + HPAGE_PMD_NR; _pte +=3D nr_ptes, + for (_pte =3D pte; _pte < pte + nr_pages; _pte +=3D nr_ptes, address +=3D nr_ptes * PAGE_SIZE) { nr_ptes =3D 1; pteval =3D ptep_get(_pte); @@ -743,13 +751,11 @@ static void __collapse_huge_page_copy_succeeded(pte_t= *pte, } =20 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 =3D 1UL << order; /* * Re-establish the PMD to point to the original page table * entry. Restoring PMD needs to be done prior to releasing @@ -763,7 +769,7 @@ 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); } =20 /* @@ -783,16 +789,16 @@ static void __collapse_huge_page_copy_failed(pte_t *p= te, */ 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 =3D SCAN_SUCCEED; - + const unsigned long nr_pages =3D 1UL << order; /* * Copying pages' contents is subject to memory poison at any iteration. */ - for (i =3D 0; i < HPAGE_PMD_NR; i++) { + for (i =3D 0; i < nr_pages; i++) { pte_t pteval =3D ptep_get(pte + i); struct page *page =3D folio_page(folio, i); unsigned long src_addr =3D address + i * PAGE_SIZE; @@ -811,10 +817,10 @@ static enum scan_result __collapse_huge_page_copy(pte= _t *pte, struct folio *foli =20 if (likely(result =3D=3D 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); =20 return result; } @@ -985,12 +991,12 @@ 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 =3D 0; vm_fault_t ret =3D 0; - unsigned long addr, end =3D start_addr + (HPAGE_PMD_NR * PAGE_SIZE); + unsigned long addr, end =3D start_addr + (PAGE_SIZE << order); enum scan_result result; pte_t *pte =3D NULL; spinlock_t *ptl; @@ -1022,6 +1028,19 @@ static enum scan_result __collapse_huge_page_swapin(= struct mm_struct *mm, pte_present(vmf.orig_pte)) continue; =20 + /* + * 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 =3D SCAN_EXCEED_SWAP_PTE; + goto out; + } + vmf.pte =3D pte; vmf.ptl =3D ptl; ret =3D do_swap_page(&vmf); @@ -1141,7 +1160,7 @@ static enum scan_result collapse_huge_page(struct mm_= struct *mm, unsigned long a * that case. Continuing to collapse causes inconsistency. */ result =3D __collapse_huge_page_swapin(mm, vma, address, pmd, - referenced); + referenced, HPAGE_PMD_ORDER); if (result !=3D SCAN_SUCCEED) goto out_nolock; } @@ -1189,6 +1208,7 @@ static enum scan_result collapse_huge_page(struct mm_= struct *mm, unsigned long a pte =3D pte_offset_map_lock(mm, &_pmd, address, &pte_ptl); if (pte) { result =3D __collapse_huge_page_isolate(vma, address, pte, cc, + HPAGE_PMD_ORDER, &compound_pagelist); spin_unlock(pte_ptl); } else { @@ -1219,6 +1239,7 @@ static enum scan_result collapse_huge_page(struct mm_= struct *mm, unsigned long a =20 result =3D __collapse_huge_page_copy(pte, folio, pmd, _pmd, vma, address, pte_ptl, + HPAGE_PMD_ORDER, &compound_pagelist); pte_unmap(pte); if (unlikely(result !=3D SCAN_SUCCEED)) --=20 2.53.0