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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id af79cd13be357-930b545e47bsm957792285a.35.2026.07.20.12.36.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 20 Jul 2026 12:36:02 -0700 (PDT) From: Gregory Price To: linux-mm@kvack.org Cc: Zhigang.Luo@amd.com, arun.george@samsung.com, balbirs@nvidia.com, brendan.jackman@linux.dev, yuzenghui@huawei.com, apopple@nvidia.com, alucerop@amd.com, matthew.brost@intel.com, akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, corbet@lwn.net, skhan@linuxfoundation.org, gregkh@linuxfoundation.org, rafael@kernel.org, dakr@kernel.org, djbw@kernel.org, vishal.l.verma@intel.com, dave.jiang@intel.com, alison.schofield@intel.com, osandov@osandov.com, jannh@google.com, pfalcato@suse.de, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, pbonzini@redhat.com, osalvador@suse.de, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, kasong@tencent.com, qi.zheng@linux.dev, shakeel.butt@linux.dev, baohua@kernel.org, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, yury.norov@gmail.com, linux@rasmusvillemoes.dk, longman@redhat.com, ridong.chen@linux.dev, tj@kernel.org, mkoutny@suse.com, sj@kernel.org, jgg@ziepe.ca, jhubbard@nvidia.com, peterx@redhat.com, baolin.wang@linux.alibaba.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, lance.yang@linux.dev, usama.arif@linux.dev, xu.xin16@zte.com.cn, chengming.zhou@linux.dev, roman.gushchin@linux.dev, muchun.song@linux.dev, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, driver-core@lists.linux.dev, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-debuggers@vger.kernel.org, linux-fsdevel@vger.kernel.org, kvm@vger.kernel.org, cgroups@vger.kernel.org, damon@lists.linux.dev, linux-kselftest@vger.kernel.org, kernel-team@meta.com Subject: [PATCH v5 32/36] mm/khugepaged: base private node collapse eligiblity on actor/cap bits Date: Mon, 20 Jul 2026 15:34:26 -0400 Message-ID: <20260720193431.3841992-33-gourry@gourry.net> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260720193431.3841992-1-gourry@gourry.net> References: <20260720193431.3841992-1-gourry@gourry.net> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Collapse can move base pages across nodes. The khugepaged daemon does this transparently, while MADV_COLLAPSE is a userland construct. Isolate private nodes from khugepaged exactly like ZONE_DEVICE. Never collapse private node folios silently (the owner may not support migration). MADV_COLLAPSE is user-initiated, so it is allowed on a private node opted into CAP_USER_NUMA, consistent with other userspace interfaces. folio_allows_collapse() encodes this: false for khugepaged on a private node, CAP_USER_NUMA for MADV_COLLAPSE. Signed-off-by: Gregory Price --- mm/internal.h | 26 ++++++++++++++++++++++++++ mm/khugepaged.c | 16 +++++++++++++--- 2 files changed, 39 insertions(+), 3 deletions(-) diff --git a/mm/internal.h b/mm/internal.h index 9621eb127c28c..9dbc5752cd3fe 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -136,6 +136,32 @@ static inline bool folio_allows_numa_balance(struct folio *folio) node_allows_numa_balancing(folio_nid(folio)); } +/* + * folio_allows_collapse() - may collapse fold this folio into a THP? + * @is_khugepaged: true for the khugepaged, false for MADV_COLLAPSE. + * + * Collapse is a residency operation gated by the actor calling it: + * - khugepaged never operates on private-node folios (like ZONE_DEVICE) + * - MADV_COLLAPSE is gated by CAP_USER_NUMA + * + * Never true for ZONE_DEVICE. + */ +static inline bool folio_allows_collapse(struct folio *folio, bool is_khugepaged) +{ + int nid = folio_nid(folio); + + if (folio_is_zone_device(folio)) + return false; + if (is_khugepaged) + return !node_is_private(nid); + return node_allows_user_numa(nid); +} + +static inline bool page_allows_collapse(struct page *page, bool is_khugepaged) +{ + return folio_allows_collapse(page_folio(page), is_khugepaged); +} + /* * folio_allows_longterm_pin() - may this folio be long-term GUP-pinned? * diff --git a/mm/khugepaged.c b/mm/khugepaged.c index fb4378cc17b10..5f20839857738 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -700,7 +700,8 @@ static enum scan_result __collapse_huge_page_isolate(struct vm_area_struct *vma, goto out; } page = vm_normal_page(vma, addr, pteval); - if (unlikely(!page) || unlikely(page_is_private_managed(page))) { + if (unlikely(!page) || + unlikely(!page_allows_collapse(page, cc->is_khugepaged))) { result = SCAN_PAGE_NULL; goto out; } @@ -1241,9 +1242,17 @@ static enum scan_result alloc_charge_folio(struct folio **foliop, struct mm_stru gfp_t gfp = (cc->is_khugepaged ? alloc_hugepage_khugepaged_gfpmask() : GFP_TRANSHUGE); int node = collapse_find_target_node(cc); + unsigned int aflags; struct folio *folio; + bool allow; - folio = __folio_alloc(gfp, order, node, &cc->alloc_nmask, ALLOC_DEFAULT); + /* Private node access: khugepaged never, madvise with CAP_USER_NUMA */ + allow = cc->is_khugepaged ? !node_is_private(node) + : node_allows_user_numa(node); + aflags = (allow && node_is_private(node)) ? + ALLOC_ZONELIST_PRIVATE : ALLOC_DEFAULT; + + folio = __folio_alloc(gfp, order, node, &cc->alloc_nmask, aflags); if (!folio) { *foliop = NULL; if (is_pmd_order(order)) @@ -1687,7 +1696,8 @@ static enum scan_result collapse_scan_pmd(struct mm_struct *mm, } page = vm_normal_page(vma, addr, pteval); - if (unlikely(!page) || unlikely(page_is_private_managed(page))) { + if (unlikely(!page) || + unlikely(!page_allows_collapse(page, cc->is_khugepaged))) { result = SCAN_PAGE_NULL; goto out_unmap; } -- 2.53.0-Meta