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[96.255.20.138]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8cb8d0ebcd0sm845419885a.28.2026.02.23.06.54.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 Feb 2026 06:55:06 -0800 (PST) Date: Mon, 23 Feb 2026 09:54:55 -0500 From: Gregory Price To: "David Hildenbrand (Arm)" Cc: lsf-pc@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, damon@lists.linux.dev, kernel-team@meta.com, gregkh@linuxfoundation.org, rafael@kernel.org, dakr@kernel.org, dave@stgolabs.net, jonathan.cameron@huawei.com, dave.jiang@intel.com, alison.schofield@intel.com, vishal.l.verma@intel.com, ira.weiny@intel.com, dan.j.williams@intel.com, longman@redhat.com, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, osalvador@suse.de, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, ying.huang@linux.alibaba.com, apopple@nvidia.com, axelrasmussen@google.com, yuanchu@google.com, weixugc@google.com, yury.norov@gmail.com, linux@rasmusvillemoes.dk, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, tj@kernel.org, hannes@cmpxchg.org, mkoutny@suse.com, jackmanb@google.com, sj@kernel.org, baolin.wang@linux.alibaba.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, muchun.song@linux.dev, xu.xin16@zte.com.cn, chengming.zhou@linux.dev, jannh@google.com, linmiaohe@huawei.com, nao.horiguchi@gmail.com, pfalcato@suse.de, rientjes@google.com, shakeel.butt@linux.dev, riel@surriel.com, harry.yoo@oracle.com, cl@gentwo.org, roman.gushchin@linux.dev, chrisl@kernel.org, kasong@tencent.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, zhengqi.arch@bytedance.com, terry.bowman@amd.com Subject: Re: [LSF/MM/BPF TOPIC][RFC PATCH v4 00/27] Private Memory Nodes (w/ Compressed RAM) Message-ID: References: <20260222084842.1824063-1-gourry@gourry.net> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Feb 23, 2026 at 02:07:15PM +0100, David Hildenbrand (Arm) wrote: > > > > Gregory Price (27): > > numa: introduce N_MEMORY_PRIVATE node state > > mm,cpuset: gate allocations from N_MEMORY_PRIVATE behind __GFP_PRIVATE > > mm/page_alloc: add numa_zone_allowed() and wire it up > > mm/page_alloc: Add private node handling to build_zonelists > > mm: introduce folio_is_private_managed() unified predicate > > mm/mlock: skip mlock for managed-memory folios > > mm/madvise: skip madvise for managed-memory folios > > mm/ksm: skip KSM for managed-memory folios > > mm/khugepaged: skip private node folios when trying to collapse. > > mm/swap: add free_folio callback for folio release cleanup > > mm/huge_memory.c: add private node folio split notification callback > > mm/migrate: NP_OPS_MIGRATION - support private node user migration > > mm/mempolicy: NP_OPS_MEMPOLICY - support private node mempolicy > > mm/memory-tiers: NP_OPS_DEMOTION - support private node demotion > > mm/mprotect: NP_OPS_PROTECT_WRITE - gate PTE/PMD write-upgrades > > I'm concerned about adding more special-casing (similar to what we already > added for ZONE_DEVICE) all over the place. > > Like the whole folio_managed_() stuff in mprotect.c > > Having that said, sounds like a reasonable topic to discuss. > It's a valid concern - and is why I tried to re-use as many of the zone_device hooks as possible. It does not seem zone_device has quite the same semantics for a case like this, so I had to make something new. DEVICE_COHERENT injects a temporary swap entry to allow the device to do a large atomic operation - then the page table is restored and the CPU is free to change entries as it pleases. Another option would be to add the hook to vma_wants_writenotify() instead of the page table code - and mask MM_CP_TRY_CHANGE_WRITABLE. This would require adding a vma flag - or maybe a count of protected / device pages. int mprotect_fixup() { ... if (vma_wants_manual_pte_write_upgrade(vma)) mm_cp_flags |= MM_CP_TRY_CHANGE_WRITABLE; } bool vma_wants_writenotify(struct vm_area_struct *vma, pgprot_t vm_page_prot) { if (vma->managed_wrprotect) return true; } That would localize the change in folio_managed_fixup_migration_pte() : static inline pte_t folio_managed_fixup_migration_pte(struct page *new, pte_t pte, pte_t old_pte, struct vm_area_struct *vma) { ... } else if (folio_managed_wrprotect(page_folio(new))) { pte = pte_wrprotect(pte); + atomic_inc(&vma->managed_wrprotect); } return pte; } This would cover both the huge_memory.c and mprotect, and maybe that's just generally cleaner? I can try that to see if it actually works. ~Gregory