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Thu, 12 Feb 2026 07:55:40 -0800 (PST) From: Joshua Hahn To: Nico Pache Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, 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, jackmanb@google.com, jack@suse.cz, 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, 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: Re: [PATCH mm-unstable v1 1/5] mm: consolidate anonymous folio PTE mapping into helpers Date: Thu, 12 Feb 2026 07:55:38 -0800 Message-ID: <20260212155539.2083102-1-joshua.hahnjy@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260212021835.17755-2-npache@redhat.com> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam12 X-Stat-Signature: ywp5ytb7e75oui1i4ysbhdthg1fsmiz8 X-Rspamd-Queue-Id: AACAEC000C X-Rspam-User: X-HE-Tag: 1770911742-105085 X-HE-Meta: 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 7RNEnRz+ dUvSirdpIo6/0cCUm3OTeZa+nwVXzQr0VcjoM2hu9m2pFtWcCyjxCkVhIfHZe0QWw5Pq6mJ83gQt249VjkDwHbLfSkcNE5kHcIFBMMb4lQxpvD8cVpkMdcnx0Gn22Lj2BcTiZIZJQsZRIyc0glpthdKl34/kojbgzf0PgQ4B//2usxLU6gLD303Nw+C8wP+dMQUVQvscl73xUPocsoD+28wZ/rW4JlDT8Up1VuVpQitEzqQioLO8I42+wwIIpuwW9flCuv7uVTknFW/1AI1DYQ8TgQ3PgOG+0NUsOZsijWp08PUKHUD5k5TXnt5WRGc2pmVUJY6JAxbF7QKNS03x3sBBUXmGixiuiScd0CEZZb/+6ei2Znca4w3qhpmEttfCFxgkLf8djaswUt8xzWz1VTZCldCngXqu6OeOW7EoDH4Q08LCyTKFThpylXpPjWlql1ndv8v8BAn2wkDgblQ2qaLNtVDFpEq6o5Y2gpqziA+ca1Jn2a29tewg5MjtlzqroaIgfeweJtY07M9vx5i8D1jg8frxhp0ZmbP7MKqeGaQK8Ij+tiImNmGphAmuEkR7ufeT2+QXl9X17WP9FVCSZEJG8WD7bqj5LuUK9 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: On Wed, 11 Feb 2026 19:18:31 -0700 Nico Pache wrote: Hello Nico, Thank you for the patch! I hope you are having a good day. > The anonymous page fault handler in do_anonymous_page() open-codes the > sequence to map a newly allocated anonymous folio at the PTE level: > - construct the PTE entry > - add rmap > - add to LRU > - set the PTEs > - update the MMU cache. > > Introduce a two helpers to consolidate this duplicated logic, mirroring the > existing map_anon_folio_pmd_nopf() pattern for PMD-level mappings: > > map_anon_folio_pte_nopf(): constructs the PTE entry, takes folio > references, adds anon rmap and LRU. This function also handles the > uffd_wp that can occur in the pf variant. > > map_anon_folio_pte_pf(): extends the nopf variant to handle MM_ANONPAGES > counter updates, and mTHP fault allocation statistics for the page fault > path. > > The zero-page read path in do_anonymous_page() is also untangled from the > shared setpte label, since it does not allocate a folio and should not > share the same mapping sequence as the write path. Make nr_pages = 1 > rather than relying on the variable. This makes it more clear that we > are operating on the zero page only. > > This refactoring will also help reduce code duplication between mm/memory.c > and mm/khugepaged.c, and provides a clean API for PTE-level anonymous folio > mapping that can be reused by future callers. It seems that based on this description, there should be no functional change in the code below. Is that correct? > Signed-off-by: Nico Pache > --- > include/linux/mm.h | 4 ++++ > mm/memory.c | 56 ++++++++++++++++++++++++++++++---------------- > 2 files changed, 41 insertions(+), 19 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index f8a8fd47399c..c3aa1f51e020 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -4916,4 +4916,8 @@ static inline bool snapshot_page_is_faithful(const struct page_snapshot *ps) > > void snapshot_page(struct page_snapshot *ps, const struct page *page); > > +void map_anon_folio_pte_nopf(struct folio *folio, pte_t *pte, > + struct vm_area_struct *vma, unsigned long addr, > + bool uffd_wp); > + > #endif /* _LINUX_MM_H */ > diff --git a/mm/memory.c b/mm/memory.c > index 8c19af97f0a0..61c2277c9d9f 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -5211,6 +5211,35 @@ static struct folio *alloc_anon_folio(struct vm_fault *vmf) > return folio_prealloc(vma->vm_mm, vma, vmf->address, true); > } > > + ^^^ extra newline? > +void map_anon_folio_pte_nopf(struct folio *folio, pte_t *pte, > + struct vm_area_struct *vma, unsigned long addr, > + bool uffd_wp) > +{ > + pte_t entry = folio_mk_pte(folio, vma->vm_page_prot); > + unsigned int nr_pages = folio_nr_pages(folio); Just reading through the code below on what was deleted and what was added, Maybe we are missing a pte_sw_mkyoung(entry) here? Seems like this would matter for MIPS systmes, but I couldn't find this change in the changelog. > + entry = maybe_mkwrite(pte_mkdirty(entry), vma); > + if (uffd_wp) > + entry = pte_mkuffd_wp(entry); The ordering here was also changed, but it wasn't immediately obvious to me why it was changed. > + > + folio_ref_add(folio, nr_pages - 1); > + folio_add_new_anon_rmap(folio, vma, addr, RMAP_EXCLUSIVE); > + folio_add_lru_vma(folio, vma); > + set_ptes(vma->vm_mm, addr, pte, entry, nr_pages); > + update_mmu_cache_range(NULL, vma, addr, pte, nr_pages); > +} > + > +static void map_anon_folio_pte_pf(struct folio *folio, pte_t *pte, > + struct vm_area_struct *vma, unsigned long addr, > + unsigned int nr_pages, bool uffd_wp) > +{ > + map_anon_folio_pte_nopf(folio, pte, vma, addr, uffd_wp); > + add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr_pages); > + count_mthp_stat(folio_order(folio), MTHP_STAT_ANON_FAULT_ALLOC); > +} > + > + ^^^ extra newline? > /* > * We enter with non-exclusive mmap_lock (to exclude vma changes, > * but allow concurrent faults), and pte mapped but not yet locked. > @@ -5257,7 +5286,13 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf) > pte_unmap_unlock(vmf->pte, vmf->ptl); > return handle_userfault(vmf, VM_UFFD_MISSING); > } > - goto setpte; > + if (vmf_orig_pte_uffd_wp(vmf)) > + entry = pte_mkuffd_wp(entry); > + set_pte_at(vma->vm_mm, addr, vmf->pte, entry); > + > + /* No need to invalidate - it was non-present before */ > + update_mmu_cache_range(vmf, vma, addr, vmf->pte, /*nr_pages=*/ 1); NIT: Should we try to keep the line under 80 columns? ; -) > + goto unlock; > } > > /* Allocate our own private page. */ > @@ -5281,11 +5316,6 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf) > */ > __folio_mark_uptodate(folio); > > - entry = folio_mk_pte(folio, vma->vm_page_prot); > - entry = pte_sw_mkyoung(entry); > - if (vma->vm_flags & VM_WRITE) > - entry = pte_mkwrite(pte_mkdirty(entry), vma); > - > vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, addr, &vmf->ptl); > if (!vmf->pte) > goto release; > @@ -5307,19 +5337,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf) > folio_put(folio); > return handle_userfault(vmf, VM_UFFD_MISSING); > } > - > - folio_ref_add(folio, nr_pages - 1); > - add_mm_counter(vma->vm_mm, MM_ANONPAGES, nr_pages); > - count_mthp_stat(folio_order(folio), MTHP_STAT_ANON_FAULT_ALLOC); > - folio_add_new_anon_rmap(folio, vma, addr, RMAP_EXCLUSIVE); > - folio_add_lru_vma(folio, vma); > -setpte: > - if (vmf_orig_pte_uffd_wp(vmf)) > - entry = pte_mkuffd_wp(entry); > - set_ptes(vma->vm_mm, addr, vmf->pte, entry, nr_pages); > - > - /* No need to invalidate - it was non-present before */ > - update_mmu_cache_range(vmf, vma, addr, vmf->pte, nr_pages); > + map_anon_folio_pte_pf(folio, vmf->pte, vma, addr, nr_pages, vmf_orig_pte_uffd_wp(vmf)); NIT: Maybe here as well? > unlock: > if (vmf->pte) > pte_unmap_unlock(vmf->pte, vmf->ptl); > -- > 2.53.0 Thank you for the patch again. I hope you have a great day! Joshua