David Hildenbrand <david@xxxxxxxxxx> writes: > On 27.06.24 02:54, Alistair Popple wrote: >> Currently DAX folio/page reference counts are managed differently to >> normal pages. To allow these to be managed the same as normal pages >> introduce dax_insert_pfn_pud. This will map the entire PUD-sized folio >> and take references as it would for a normally mapped page. >> This is distinct from the current mechanism, vmf_insert_pfn_pud, >> which >> simply inserts a special devmap PUD entry into the page table without >> holding a reference to the page for the mapping. > > Do we really have to involve mapcounts/rmap for daxfs pages at this > point? Or is this only "to make it look more like other pages" ? The aim of the series is make FS DAX and other ZONE_DEVICE pages look like other pages, at least with regards to the way they are refcounted. At the moment they are not refcounted - instead their refcounts are basically statically initialised to one and there are all these special cases and functions requiring magic PTE bits (pXX_devmap) to do the special DAX reference counting. This then adds some cruft to manage pgmap references and to catch the 2->1 page refcount transition. All this just goes away if we manage the page references the same as other pages (and indeed we already manage DEVICE_PRIVATE and COHERENT pages the same as normal pages). So I think to make this work we at least need the mapcounts. > I'm asking this because: > > (A) We don't support mixing PUD+PMD mappings yet. I have plans to change > that in the future, but for now you can only map using a single PUD > or by PTEs. I suspect that's good enoug for now for dax fs? Yep, that's all we support. > (B) As long as we have subpage mapcounts, this prevents vmemmap > optimizations [1]. Is that only used for device-dax for now and are > there no plans to make use of that for fs-dax? I don't have any plans to. This is purely focussed on refcounting pages "like normal" so we can get rid of all the DAX special casing. > (C) We managed without so far :) Indeed, although Christoph has asked repeatedly ([1], [2] and likely others) that this gets fixed and I finally got sick of it coming up everytime I need to touch something with ZONE_DEVICE pages :) Also it removes the need for people to understand the special DAX page recounting scheme and ends up removing a bunch of cruft as a bonus: 59 files changed, 485 insertions(+), 869 deletions(-) And that's before I clean up all the pgmap reference handling. It also removes the pXX_trans_huge and pXX_leaf distinction. So we managed, but things could be better IMHO. > Having that said, with folio->_large_mapcount things like > folio_mapcount() are no longer terribly slow once we weould PTE-map a > PUD-sized folio. > > Also, all ZONE_DEVICE pages should currently be marked PG_reserved, > translating to "don't touch the memmap". I think we might want to > tackle that first. Ok. I'm keen to get this series finished and I don't quite get the connection here, what needs to change there? [1] - https://lore.kernel.org/linux-mm/20201106080322.GE31341@xxxxxx/ [2] - https://lore.kernel.org/linux-mm/20220209135351.GA20631@xxxxxx/ > > [1] https://lwn.net/Articles/860218/ > [2] > https://lkml.kernel.org/r/b0adbb0c-ad59-4bc5-ba0b-0af464b94557@xxxxxxxxxx > >> Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx> >> --- >> include/linux/huge_mm.h | 4 ++- >> include/linux/rmap.h | 14 +++++- >> mm/huge_memory.c | 108 ++++++++++++++++++++++++++++++++++++++--- >> mm/rmap.c | 48 ++++++++++++++++++- >> 4 files changed, 168 insertions(+), 6 deletions(-) >> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >> index 2aa986a..b98a3cc 100644 >> --- a/include/linux/huge_mm.h >> +++ b/include/linux/huge_mm.h >> @@ -39,6 +39,7 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, >> vm_fault_t vmf_insert_pfn_pmd(struct vm_fault *vmf, pfn_t pfn, >> bool write); >> vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write); >> +vm_fault_t dax_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write); >> enum transparent_hugepage_flag { >> TRANSPARENT_HUGEPAGE_UNSUPPORTED, >> @@ -106,6 +107,9 @@ extern struct kobj_attribute shmem_enabled_attr; >> #define HPAGE_PUD_MASK (~(HPAGE_PUD_SIZE - 1)) >> #define HPAGE_PUD_SIZE ((1UL) << HPAGE_PUD_SHIFT) >> +#define HPAGE_PUD_ORDER (HPAGE_PUD_SHIFT-PAGE_SHIFT) >> +#define HPAGE_PUD_NR (1<<HPAGE_PUD_ORDER) >> + >> #ifdef CONFIG_TRANSPARENT_HUGEPAGE >> extern unsigned long transparent_hugepage_flags; >> diff --git a/include/linux/rmap.h b/include/linux/rmap.h >> index 7229b9b..c5a0205 100644 >> --- a/include/linux/rmap.h >> +++ b/include/linux/rmap.h >> @@ -192,6 +192,7 @@ typedef int __bitwise rmap_t; >> enum rmap_level { >> RMAP_LEVEL_PTE = 0, >> RMAP_LEVEL_PMD, >> + RMAP_LEVEL_PUD, >> }; >> static inline void __folio_rmap_sanity_checks(struct folio >> *folio, >> @@ -225,6 +226,13 @@ static inline void __folio_rmap_sanity_checks(struct folio *folio, >> VM_WARN_ON_FOLIO(folio_nr_pages(folio) != HPAGE_PMD_NR, folio); >> VM_WARN_ON_FOLIO(nr_pages != HPAGE_PMD_NR, folio); >> break; >> + case RMAP_LEVEL_PUD: >> + /* >> + * Asume that we are creating * a single "entire" mapping of the folio. >> + */ >> + VM_WARN_ON_FOLIO(folio_nr_pages(folio) != HPAGE_PUD_NR, folio); >> + VM_WARN_ON_FOLIO(nr_pages != HPAGE_PUD_NR, folio); >> + break; >> default: >> VM_WARN_ON_ONCE(true); >> } >> @@ -248,12 +256,16 @@ void folio_add_file_rmap_ptes(struct folio *, struct page *, int nr_pages, >> folio_add_file_rmap_ptes(folio, page, 1, vma) >> void folio_add_file_rmap_pmd(struct folio *, struct page *, >> struct vm_area_struct *); >> +void folio_add_file_rmap_pud(struct folio *, struct page *, >> + struct vm_area_struct *); >> void folio_remove_rmap_ptes(struct folio *, struct page *, int nr_pages, >> struct vm_area_struct *); >> #define folio_remove_rmap_pte(folio, page, vma) \ >> folio_remove_rmap_ptes(folio, page, 1, vma) >> void folio_remove_rmap_pmd(struct folio *, struct page *, >> struct vm_area_struct *); >> +void folio_remove_rmap_pud(struct folio *, struct page *, >> + struct vm_area_struct *); >> void hugetlb_add_anon_rmap(struct folio *, struct vm_area_struct >> *, >> unsigned long address, rmap_t flags); >> @@ -338,6 +350,7 @@ static __always_inline void __folio_dup_file_rmap(struct folio *folio, >> atomic_add(orig_nr_pages, &folio->_large_mapcount); >> break; >> case RMAP_LEVEL_PMD: >> + case RMAP_LEVEL_PUD: >> atomic_inc(&folio->_entire_mapcount); >> atomic_inc(&folio->_large_mapcount); >> break; >> @@ -434,6 +447,7 @@ static __always_inline int __folio_try_dup_anon_rmap(struct folio *folio, >> atomic_add(orig_nr_pages, &folio->_large_mapcount); >> break; >> case RMAP_LEVEL_PMD: >> + case RMAP_LEVEL_PUD: >> if (PageAnonExclusive(page)) { >> if (unlikely(maybe_pinned)) >> return -EBUSY; >> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >> index db7946a..e1f053e 100644 >> --- a/mm/huge_memory.c >> +++ b/mm/huge_memory.c >> @@ -1283,6 +1283,70 @@ vm_fault_t vmf_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write) >> return VM_FAULT_NOPAGE; >> } >> EXPORT_SYMBOL_GPL(vmf_insert_pfn_pud); >> + >> +/** >> + * dax_insert_pfn_pud - insert a pud size pfn backed by a normal page >> + * @vmf: Structure describing the fault >> + * @pfn: pfn of the page to insert >> + * @write: whether it's a write fault >> + * >> + * Return: vm_fault_t value. >> + */ >> +vm_fault_t dax_insert_pfn_pud(struct vm_fault *vmf, pfn_t pfn, bool write) >> +{ >> + struct vm_area_struct *vma = vmf->vma; >> + unsigned long addr = vmf->address & PUD_MASK; >> + pud_t *pud = vmf->pud; >> + pgprot_t prot = vma->vm_page_prot; >> + struct mm_struct *mm = vma->vm_mm; >> + pud_t entry; >> + spinlock_t *ptl; >> + struct folio *folio; >> + struct page *page; >> + >> + if (addr < vma->vm_start || addr >= vma->vm_end) >> + return VM_FAULT_SIGBUS; >> + >> + track_pfn_insert(vma, &prot, pfn); >> + >> + ptl = pud_lock(mm, pud); >> + if (!pud_none(*pud)) { >> + if (write) { >> + if (pud_pfn(*pud) != pfn_t_to_pfn(pfn)) { >> + WARN_ON_ONCE(!is_huge_zero_pud(*pud)); >> + goto out_unlock; >> + } >> + entry = pud_mkyoung(*pud); >> + entry = maybe_pud_mkwrite(pud_mkdirty(entry), vma); >> + if (pudp_set_access_flags(vma, addr, pud, entry, 1)) >> + update_mmu_cache_pud(vma, addr, pud); >> + } >> + goto out_unlock; >> + } >> + >> + entry = pud_mkhuge(pfn_t_pud(pfn, prot)); >> + if (pfn_t_devmap(pfn)) >> + entry = pud_mkdevmap(entry); >> + if (write) { >> + entry = pud_mkyoung(pud_mkdirty(entry)); >> + entry = maybe_pud_mkwrite(entry, vma); >> + } >> + >> + page = pfn_t_to_page(pfn); >> + folio = page_folio(page); >> + folio_get(folio); >> + folio_add_file_rmap_pud(folio, page, vma); >> + add_mm_counter(mm, mm_counter_file(folio), HPAGE_PUD_NR); >> + >> + set_pud_at(mm, addr, pud, entry); >> + update_mmu_cache_pud(vma, addr, pud); >> + >> +out_unlock: >> + spin_unlock(ptl); >> + >> + return VM_FAULT_NOPAGE; >> +} >> +EXPORT_SYMBOL_GPL(dax_insert_pfn_pud); >> #endif /* CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */ >> void touch_pmd(struct vm_area_struct *vma, unsigned long addr, >> @@ -1836,7 +1900,8 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, >> zap_deposited_table(tlb->mm, pmd); >> spin_unlock(ptl); >> } else if (is_huge_zero_pmd(orig_pmd)) { >> - zap_deposited_table(tlb->mm, pmd); >> + if (!vma_is_dax(vma) || arch_needs_pgtable_deposit()) >> + zap_deposited_table(tlb->mm, pmd); >> spin_unlock(ptl); >> } else { >> struct folio *folio = NULL; >> @@ -2268,20 +2333,34 @@ spinlock_t *__pud_trans_huge_lock(pud_t *pud, struct vm_area_struct *vma) >> int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma, >> pud_t *pud, unsigned long addr) >> { >> + pud_t orig_pud; >> spinlock_t *ptl; >> ptl = __pud_trans_huge_lock(pud, vma); >> if (!ptl) >> return 0; >> - pudp_huge_get_and_clear_full(vma, addr, pud, tlb->fullmm); >> + orig_pud = pudp_huge_get_and_clear_full(vma, addr, pud, tlb->fullmm); >> tlb_remove_pud_tlb_entry(tlb, pud, addr); >> - if (vma_is_special_huge(vma)) { >> + if (!vma_is_dax(vma) && vma_is_special_huge(vma)) { >> spin_unlock(ptl); >> /* No zero page support yet */ >> } else { >> - /* No support for anonymous PUD pages yet */ >> - BUG(); >> + struct page *page = NULL; >> + struct folio *folio; >> + >> + /* No support for anonymous PUD pages or migration yet */ >> + BUG_ON(vma_is_anonymous(vma) || !pud_present(orig_pud)); >> + >> + page = pud_page(orig_pud); >> + folio = page_folio(page); >> + folio_remove_rmap_pud(folio, page, vma); >> + VM_BUG_ON_PAGE(page_mapcount(page) < 0, page); >> + VM_BUG_ON_PAGE(!PageHead(page), page); >> + add_mm_counter(tlb->mm, mm_counter_file(folio), -HPAGE_PUD_NR); >> + >> + spin_unlock(ptl); >> + tlb_remove_page_size(tlb, page, HPAGE_PUD_SIZE); >> } >> return 1; >> } >> @@ -2289,6 +2368,8 @@ int zap_huge_pud(struct mmu_gather *tlb, struct vm_area_struct *vma, >> static void __split_huge_pud_locked(struct vm_area_struct *vma, pud_t *pud, >> unsigned long haddr) >> { >> + pud_t old_pud; >> + >> VM_BUG_ON(haddr & ~HPAGE_PUD_MASK); >> VM_BUG_ON_VMA(vma->vm_start > haddr, vma); >> VM_BUG_ON_VMA(vma->vm_end < haddr + HPAGE_PUD_SIZE, vma); >> @@ -2296,7 +2377,22 @@ static void __split_huge_pud_locked(struct vm_area_struct *vma, pud_t *pud, >> count_vm_event(THP_SPLIT_PUD); >> - pudp_huge_clear_flush(vma, haddr, pud); >> + old_pud = pudp_huge_clear_flush(vma, haddr, pud); >> + if (is_huge_zero_pud(old_pud)) >> + return; >> + >> + if (vma_is_dax(vma)) { >> + struct page *page = pud_page(old_pud); >> + struct folio *folio = page_folio(page); >> + >> + if (!folio_test_dirty(folio) && pud_dirty(old_pud)) >> + folio_mark_dirty(folio); >> + if (!folio_test_referenced(folio) && pud_young(old_pud)) >> + folio_set_referenced(folio); >> + folio_remove_rmap_pud(folio, page, vma); >> + folio_put(folio); >> + add_mm_counter(vma->vm_mm, mm_counter_file(folio), -HPAGE_PUD_NR); >> + } >> } >> void __split_huge_pud(struct vm_area_struct *vma, pud_t *pud, >> diff --git a/mm/rmap.c b/mm/rmap.c >> index e8fc5ec..e949e4f 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -1165,6 +1165,7 @@ static __always_inline unsigned int __folio_add_rmap(struct folio *folio, >> atomic_add(orig_nr_pages, &folio->_large_mapcount); >> break; >> case RMAP_LEVEL_PMD: >> + case RMAP_LEVEL_PUD: >> first = atomic_inc_and_test(&folio->_entire_mapcount); >> if (first) { >> nr = atomic_add_return_relaxed(ENTIRELY_MAPPED, mapped); >> @@ -1306,6 +1307,12 @@ static __always_inline void __folio_add_anon_rmap(struct folio *folio, >> case RMAP_LEVEL_PMD: >> SetPageAnonExclusive(page); >> break; >> + case RMAP_LEVEL_PUD: >> + /* >> + * Keep the compiler happy, we don't support anonymous PUD mappings. >> + */ >> + WARN_ON_ONCE(1); >> + break; >> } >> } >> for (i = 0; i < nr_pages; i++) { >> @@ -1489,6 +1496,26 @@ void folio_add_file_rmap_pmd(struct folio *folio, struct page *page, >> #endif >> } >> +/** >> + * folio_add_file_rmap_pud - add a PUD mapping to a page range of a folio >> + * @folio: The folio to add the mapping to >> + * @page: The first page to add >> + * @vma: The vm area in which the mapping is added >> + * >> + * The page range of the folio is defined by [page, page + HPAGE_PUD_NR) >> + * >> + * The caller needs to hold the page table lock. >> + */ >> +void folio_add_file_rmap_pud(struct folio *folio, struct page *page, >> + struct vm_area_struct *vma) >> +{ >> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD >> + __folio_add_file_rmap(folio, page, HPAGE_PUD_NR, vma, RMAP_LEVEL_PUD); >> +#else >> + WARN_ON_ONCE(true); >> +#endif >> +} >> + >> static __always_inline void __folio_remove_rmap(struct folio *folio, >> struct page *page, int nr_pages, struct vm_area_struct *vma, >> enum rmap_level level) >> @@ -1521,6 +1548,7 @@ static __always_inline void __folio_remove_rmap(struct folio *folio, >> partially_mapped = nr && atomic_read(mapped); >> break; >> case RMAP_LEVEL_PMD: >> + case RMAP_LEVEL_PUD: >> atomic_dec(&folio->_large_mapcount); >> last = atomic_add_negative(-1, &folio->_entire_mapcount); >> if (last) { >> @@ -1615,6 +1643,26 @@ void folio_remove_rmap_pmd(struct folio *folio, struct page *page, >> #endif >> } >> +/** >> + * folio_remove_rmap_pud - remove a PUD mapping from a page range of a folio >> + * @folio: The folio to remove the mapping from >> + * @page: The first page to remove >> + * @vma: The vm area from which the mapping is removed >> + * >> + * The page range of the folio is defined by [page, page + HPAGE_PUD_NR) >> + * >> + * The caller needs to hold the page table lock. >> + */ >> +void folio_remove_rmap_pud(struct folio *folio, struct page *page, >> + struct vm_area_struct *vma) >> +{ >> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD >> + __folio_remove_rmap(folio, page, HPAGE_PUD_NR, vma, RMAP_LEVEL_PUD); >> +#else >> + WARN_ON_ONCE(true); >> +#endif >> +} >> + >> /* >> * @arg: enum ttu_flags will be passed to this argument >> */
