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Howlett , ryan.roberts@arm.com, Vlastimil Babka , lance.yang@linux.dev, linux-kernel@vger.kernel.org, nphamcs@gmail.com, shikemeng@huaweicloud.com, yosry@kernel.org, qi.zheng@linux.dev, luizcap@redhat.com, kernel-team@meta.com, Usama Arif Subject: [PATCH v9 11/32] mm: make PMD migration-entry splitting explicit Date: Thu, 5 Nov 2026 10:38:55 -0800 Message-ID: <20261105183940.2236717-12-usama.arif@linux.dev> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261105183940.2236717-1-usama.arif@linux.dev> References: <20261105183940.2236717-1-usama.arif@linux.dev> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit __split_huge_pmd() and friends take a "freeze" boolean that every caller has to pass and almost every caller passes as false. The name says nothing about what it selects, and the one thing it does select - PTE migration entries instead of PTE mappings - is only ever wanted by the rmap migration path. Rename it to to_migration_entries, keep it private to mm/huge_memory.c, and add split_pmd_to_migration_entries() for try_to_migrate_one(), the only caller that wants it. split_pmd_to_migration_entries() is only ever handed a present or device-private PMD, so assert that in __split_huge_pmd_locked() instead of silently skipping anything else. Other than that assertion, no functional change intended. Suggested-by: David Hildenbrand (Arm) Signed-off-by: Usama Arif Reviewed-by: Kiryl Shutsemau (Meta) --- include/linux/huge_mm.h | 21 ++++++------ mm/huge_memory.c | 74 ++++++++++++++++++++++++++--------------- mm/memory.c | 4 +-- mm/migrate_device.c | 2 +- mm/mprotect.c | 2 +- mm/rmap.c | 8 ++--- 6 files changed, 65 insertions(+), 46 deletions(-) diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index 421217aca4ed8..34307bda8071b 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -431,7 +431,7 @@ int folio_memcg_alloc_deferred(struct folio *folio); void deferred_split_folio(struct folio *folio, bool partially_mapped); void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, - unsigned long address, bool freeze); + unsigned long address); /** * pmd_is_huge() - Is this PMD either a huge PMD entry or a software leaf entry? @@ -463,12 +463,10 @@ static inline bool pmd_is_huge(pmd_t pmd) do { \ pmd_t *____pmd = (__pmd); \ if (pmd_is_huge(*____pmd)) \ - __split_huge_pmd(__vma, __pmd, __address, \ - false); \ + __split_huge_pmd(__vma, __pmd, __address); \ } while (0) -void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, - bool freeze); +void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address); void __split_huge_pud(struct vm_area_struct *vma, pud_t *pud, unsigned long address); @@ -593,7 +591,9 @@ static inline bool thp_migration_supported(void) } void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address, - pmd_t *pmd, bool freeze); + pmd_t *pmd); +void split_pmd_to_migration_entries(struct vm_area_struct *vma, + unsigned long address, pmd_t *pmd); bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr, pmd_t *pmdp, struct folio *folio); void map_anon_folio_pmd_nopf(struct folio *folio, pmd_t *pmd, @@ -693,12 +693,13 @@ static inline void deferred_split_folio(struct folio *folio, bool partially_mapp do { } while (0) static inline void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, - unsigned long address, bool freeze) {} + unsigned long address) {} static inline void split_huge_pmd_address(struct vm_area_struct *vma, - unsigned long address, bool freeze) {} + unsigned long address) {} static inline void split_huge_pmd_locked(struct vm_area_struct *vma, - unsigned long address, pmd_t *pmd, - bool freeze) {} + unsigned long address, pmd_t *pmd) {} +static inline void split_pmd_to_migration_entries(struct vm_area_struct *vma, + unsigned long address, pmd_t *pmd) {} static inline bool unmap_huge_pmd_locked(struct vm_area_struct *vma, unsigned long addr, pmd_t *pmdp, diff --git a/mm/huge_memory.c b/mm/huge_memory.c index e425a5b05aa2e..82a4fa9342672 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2031,7 +2031,7 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, pte_free(dst_mm, pgtable); spin_unlock(src_ptl); spin_unlock(dst_ptl); - __split_huge_pmd(src_vma, src_pmd, addr, false); + __split_huge_pmd(src_vma, src_pmd, addr); return -EAGAIN; } add_mm_counter(dst_mm, MM_ANONPAGES, HPAGE_PMD_NR); @@ -2255,7 +2255,7 @@ vm_fault_t do_huge_pmd_wp_page(struct vm_fault *vmf) folio_unlock(folio); spin_unlock(vmf->ptl); fallback: - __split_huge_pmd(vma, vmf->pmd, vmf->address, false); + __split_huge_pmd(vma, vmf->pmd, vmf->address); return VM_FAULT_FALLBACK; } @@ -3176,7 +3176,7 @@ static void __split_huge_zero_page_pmd(struct vm_area_struct *vma, } static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, - unsigned long haddr, bool freeze) + unsigned long haddr, bool to_migration_entries) { struct mm_struct *mm = vma->vm_mm; struct folio *folio; @@ -3194,6 +3194,8 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PMD_SIZE, vma); VM_WARN_ON_ONCE(!pmd_is_valid_softleaf(*pmd) && !pmd_trans_huge(*pmd)); + VM_WARN_ON_ONCE(to_migration_entries && !pmd_present(*pmd) && + !pmd_is_device_private_entry(*pmd)); count_vm_event(THP_SPLIT_PMD); @@ -3277,10 +3279,10 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, * folios w.r.t anon exclusive handling. See the comments for * folio handling and anon_exclusive below. */ - if (freeze && anon_exclusive && + if (to_migration_entries && anon_exclusive && folio_try_share_anon_rmap_pmd(folio, page)) - freeze = false; - if (!freeze) { + to_migration_entries = false; + if (!to_migration_entries) { rmap_t rmap_flags = RMAP_NONE; folio_ref_add(folio, HPAGE_PMD_NR - 1); @@ -3330,13 +3332,14 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, VM_WARN_ON_FOLIO(!folio_test_anon(folio), folio); /* - * Without "freeze", we'll simply split the PMD, propagating the - * PageAnonExclusive() flag for each PTE by setting it for - * each subpage -- no need to (temporarily) clear. + * When not splitting to migration entries, we'll simply split + * the PMD and propagate the PageAnonExclusive() flag for each + * PTE by setting it for each page -- no need to (temporarily) + * clear. * - * With "freeze" we want to replace mapped pages by - * migration entries right away. This is only possible if we - * managed to clear PageAnonExclusive() -- see + * When splitting to migration entries, we want to replace + * mapped pages by migration entries right away. This is only + * possible if we managed to clear PageAnonExclusive() -- see * set_pmd_migration_entry(). * * In case we cannot clear PageAnonExclusive(), split the PMD @@ -3345,10 +3348,10 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, * See folio_try_share_anon_rmap_pmd(): invalidate PMD first. */ anon_exclusive = PageAnonExclusive(page); - if (freeze && anon_exclusive && + if (to_migration_entries && anon_exclusive && folio_try_share_anon_rmap_pmd(folio, page)) - freeze = false; - if (!freeze) { + to_migration_entries = false; + if (!to_migration_entries) { rmap_t rmap_flags = RMAP_NONE; folio_ref_add(folio, HPAGE_PMD_NR - 1); @@ -3373,7 +3376,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, * Note that NUMA hinting access restrictions are not transferred to * avoid any possibility of altering permissions across VMAs. */ - if (freeze || pmd_is_migration_entry(old_pmd)) { + if (to_migration_entries || pmd_is_migration_entry(old_pmd)) { pte_t entry; swp_entry_t swp_entry; @@ -3406,8 +3409,8 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) { /* * anon_exclusive was already propagated to the relevant - * pages corresponding to the pte entries when freeze - * is false. + * pages corresponding to the pte entries when + * to_migration_entries is false. */ if (write) swp_entry = make_writable_device_private_entry( @@ -3455,7 +3458,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, if (!pmd_is_migration_entry(*pmd)) folio_remove_rmap_pmd(folio, page, vma); - if (freeze) + if (to_migration_entries) put_page(page); smp_wmb(); /* make pte visible before pmd */ @@ -3463,15 +3466,33 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, } void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address, - pmd_t *pmd, bool freeze) + pmd_t *pmd) { VM_WARN_ON_ONCE(!IS_ALIGNED(address, HPAGE_PMD_SIZE)); if (pmd_trans_huge(*pmd) || pmd_is_valid_softleaf(*pmd)) - __split_huge_pmd_locked(vma, pmd, address, freeze); + __split_huge_pmd_locked(vma, pmd, address, false); +} + +/** + * split_pmd_to_migration_entries() - Split a present or device private PMD into + * PTE migration entries. + * @vma: The VMA containing the PMD. + * @address: The PMD-aligned address the PMD maps. + * @pmd: A pointer to the leaf PMD entry. + * + * For the rmap migration walker, which only ever hands back those two entry + * types. Like split_huge_pmd_locked(), the caller must hold the PMD lock and + * must already be inside an mmu_notifier invalidate range. + */ +void split_pmd_to_migration_entries(struct vm_area_struct *vma, + unsigned long address, pmd_t *pmd) +{ + VM_WARN_ON_ONCE(!IS_ALIGNED(address, HPAGE_PMD_SIZE)); + __split_huge_pmd_locked(vma, pmd, address, true); } void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, - unsigned long address, bool freeze) + unsigned long address) { spinlock_t *ptl; struct mmu_notifier_range range; @@ -3481,20 +3502,19 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, (address & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE); mmu_notifier_invalidate_range_start(&range); ptl = pmd_lock(vma->vm_mm, pmd); - split_huge_pmd_locked(vma, range.start, pmd, freeze); + split_huge_pmd_locked(vma, range.start, pmd); spin_unlock(ptl); mmu_notifier_invalidate_range_end(&range); } -void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, - bool freeze) +void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address) { pmd_t *pmd = mm_find_pmd(vma->vm_mm, address); if (!pmd) return; - __split_huge_pmd(vma, pmd, address, freeze); + __split_huge_pmd(vma, pmd, address); } static inline void split_huge_pmd_if_needed(struct vm_area_struct *vma, unsigned long address) @@ -3506,7 +3526,7 @@ static inline void split_huge_pmd_if_needed(struct vm_area_struct *vma, unsigned if (!IS_ALIGNED(address, HPAGE_PMD_SIZE) && range_in_vma(vma, ALIGN_DOWN(address, HPAGE_PMD_SIZE), ALIGN(address, HPAGE_PMD_SIZE))) - split_huge_pmd_address(vma, address, false); + split_huge_pmd_address(vma, address); } void vma_adjust_trans_huge(struct vm_area_struct *vma, diff --git a/mm/memory.c b/mm/memory.c index 6fe0b7dab927c..85bd1b08a1a2a 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2099,7 +2099,7 @@ static inline unsigned long zap_pmd_range(struct mmu_gather *tlb, next = pmd_addr_end(addr, end); if (pmd_is_huge(*pmd)) { if (next - addr != HPAGE_PMD_SIZE) - __split_huge_pmd(vma, pmd, addr, false); + __split_huge_pmd(vma, pmd, addr); else if (zap_huge_pmd(tlb, vma, pmd, addr)) { addr = next; continue; @@ -6491,7 +6491,7 @@ static inline vm_fault_t wp_huge_pmd(struct vm_fault *vmf) split: /* COW or write-notify handled on pte level: split pmd. */ - __split_huge_pmd(vma, vmf->pmd, vmf->address, false); + __split_huge_pmd(vma, vmf->pmd, vmf->address); return VM_FAULT_FALLBACK; } diff --git a/mm/migrate_device.c b/mm/migrate_device.c index 3286bb8a4b73e..1096319aa8166 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -920,7 +920,7 @@ static int migrate_vma_split_unmapped_folio(struct migrate_vma *migrate, unsigned long flags; int ret = 0; - split_huge_pmd_address(migrate->vma, addr, false); + split_huge_pmd_address(migrate->vma, addr); ret = folio_split_unmapped(folio, 0); if (ret) return ret; diff --git a/mm/mprotect.c b/mm/mprotect.c index e18d4e12fc341..e0e28bbddbadd 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -530,7 +530,7 @@ static inline long change_pmd_range(struct mmu_gather *tlb, if (pmd_is_huge(_pmd)) { if ((next - addr != HPAGE_PMD_SIZE) || pgtable_split_needed(vma, cp_flags)) { - __split_huge_pmd(vma, pmd, addr, false); + __split_huge_pmd(vma, pmd, addr); /* * For file-backed, the pmd could have been * cleared; make sure pmd populated if diff --git a/mm/rmap.c b/mm/rmap.c index 1131b76bbbc28..9d6353e98e7c7 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -2280,8 +2280,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, * We temporarily have to drop the PTL and * restart so we can process the PTE-mapped THP. */ - split_huge_pmd_locked(vma, pvmw.address, - pvmw.pmd, false); + split_huge_pmd_locked(vma, pvmw.address, pvmw.pmd); flags &= ~TTU_SPLIT_HUGE_PMD; page_vma_mapped_walk_restart(&pvmw); continue; @@ -2506,13 +2505,12 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, if (flags & TTU_SPLIT_HUGE_PMD) { /* - * split_huge_pmd_locked() might leave the + * split_pmd_to_migration_entries() might leave the * folio mapped through PTEs. Retry the walk * so we can detect this scenario and properly * abort the walk. */ - split_huge_pmd_locked(vma, pvmw.address, - pvmw.pmd, true); + split_pmd_to_migration_entries(vma, pvmw.address, pvmw.pmd); flags &= ~TTU_SPLIT_HUGE_PMD; page_vma_mapped_walk_restart(&pvmw); continue; -- 2.53.0-Meta