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Although the code is > > designed to be generic when it comes to handling splitting > > of pages, the code is designed to work for THP page sizes > > corresponding to HPAGE_PMD_NR. > > > > Modify page_vma_mapped_walk() to return true when a zone > > device huge entry is present, enabling try_to_migrate() > > and other code migration paths to appropriately process the > > entry > > > > pmd_pfn() does not work well with zone device entries, use > > pfn_pmd_entry_to_swap() for checking and comparison as for > > zone device entries. > > > > try_to_map_to_unused_zeropage() does not apply to zone device > > entries, zone device entries are ignored in the call. > > > > Signed-off-by: Balbir Singh > > --- > > mm/huge_memory.c | 151 +++++++++++++++++++++++++++++++------------ > > mm/migrate.c | 2 + > > mm/page_vma_mapped.c | 10 +++ > > mm/rmap.c | 19 +++++- > > 4 files changed, 138 insertions(+), 44 deletions(-) > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index 826bfe907017..d8e018d1bdbd 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -2247,10 +2247,17 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > > } else if (thp_migration_supported()) { > > swp_entry_t entry; > > - VM_BUG_ON(!is_pmd_migration_entry(orig_pmd)); > > entry = pmd_to_swp_entry(orig_pmd); > > folio = pfn_swap_entry_folio(entry); > > flush_needed = 0; > > + > > + VM_BUG_ON(!is_pmd_migration_entry(*pmd) && > > + !folio_is_device_private(folio)); > > Convert that to a VM_WARN_ON_ONCE() while you are at it. > > But really, check that the *pmd* is as expected (device_pritavte entry), and > not the folio after the effects. > > Also, hiding all that under the thp_migration_supported() looks wrong. > > Likely you must clean that up first, to have something that expresses that > we support PMD swap entries or sth like that. Not just "migration entries". > > > > + > > + if (folio_is_device_private(folio)) { > > + folio_remove_rmap_pmd(folio, folio_page(folio, 0), vma); > > + WARN_ON_ONCE(folio_mapcount(folio) < 0); > > + } > > > zap_nonpresent_ptes() does > > if (is_device_private_entry(entry)) { > ... > } else if (is_migration_entry(entry)) { > .... > } > > Can we adjust the same way of foing things? (yes, we might want a > thp_migration_supported() check somewhere) > > > } else > > WARN_ONCE(1, "Non present huge pmd without pmd migration enabled!"); > > @@ -2264,6 +2271,15 @@ int zap_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > > -HPAGE_PMD_NR); > > } > > + /* > > + * Do a folio put on zone device private pages after > > + * changes to mm_counter, because the folio_put() will > > + * clean folio->mapping and the folio_test_anon() check > > + * will not be usable. > > + */ > > + if (folio_is_device_private(folio)) > > + folio_put(folio); > > + > > spin_unlock(ptl); > > if (flush_needed) > > tlb_remove_page_size(tlb, &folio->page, HPAGE_PMD_SIZE); > > @@ -2392,7 +2408,8 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > > struct folio *folio = pfn_swap_entry_folio(entry); > > pmd_t newpmd; > > - VM_BUG_ON(!is_pmd_migration_entry(*pmd)); > > + VM_BUG_ON(!is_pmd_migration_entry(*pmd) && > > + !folio_is_device_private(folio)); > > if (is_writable_migration_entry(entry)) { > > /* > > * A protection check is difficult so > > @@ -2405,9 +2422,11 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma, > > newpmd = swp_entry_to_pmd(entry); > > if (pmd_swp_soft_dirty(*pmd)) > > newpmd = pmd_swp_mksoft_dirty(newpmd); > > - } else { > > + } else if (is_writable_device_private_entry(entry)) { > > + newpmd = swp_entry_to_pmd(entry); > > + entry = make_device_exclusive_entry(swp_offset(entry)); > > + } else > > newpmd = *pmd; > > - } > > if (uffd_wp) > > newpmd = pmd_swp_mkuffd_wp(newpmd); > > @@ -2860,11 +2879,12 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > > struct page *page; > > pgtable_t pgtable; > > pmd_t old_pmd, _pmd; > > - bool young, write, soft_dirty, pmd_migration = false, uffd_wp = false; > > - bool anon_exclusive = false, dirty = false; > > + bool young, write, soft_dirty, uffd_wp = false; > > + bool anon_exclusive = false, dirty = false, present = false; > > unsigned long addr; > > pte_t *pte; > > int i; > > + swp_entry_t swp_entry; > > VM_BUG_ON(haddr & ~HPAGE_PMD_MASK); > > VM_BUG_ON_VMA(vma->vm_start > haddr, vma); > > @@ -2918,20 +2938,25 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > > return __split_huge_zero_page_pmd(vma, haddr, pmd); > > } > > - pmd_migration = is_pmd_migration_entry(*pmd); > > - if (unlikely(pmd_migration)) { > > - swp_entry_t entry; > > + present = pmd_present(*pmd); > > + if (unlikely(!present)) { > > + swp_entry = pmd_to_swp_entry(*pmd); > > old_pmd = *pmd; > > - entry = pmd_to_swp_entry(old_pmd); > > - page = pfn_swap_entry_to_page(entry); > > - write = is_writable_migration_entry(entry); > > + > > + folio = pfn_swap_entry_folio(swp_entry); > > + VM_BUG_ON(!is_migration_entry(swp_entry) && > > + !is_device_private_entry(swp_entry)); > > + page = pfn_swap_entry_to_page(swp_entry); > > + write = is_writable_migration_entry(swp_entry); > > + > > if (PageAnon(page)) > > - anon_exclusive = is_readable_exclusive_migration_entry(entry); > > - young = is_migration_entry_young(entry); > > - dirty = is_migration_entry_dirty(entry); > > + anon_exclusive = > > + is_readable_exclusive_migration_entry(swp_entry); > > soft_dirty = pmd_swp_soft_dirty(old_pmd); > > uffd_wp = pmd_swp_uffd_wp(old_pmd); > > + young = is_migration_entry_young(swp_entry); > > + dirty = is_migration_entry_dirty(swp_entry); > > } else { > > /* > > * Up to this point the pmd is present and huge and userland has > > @@ -3015,30 +3040,45 @@ 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_migration) { > > + if (freeze || !present) { > > for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) { > > pte_t entry; > > - swp_entry_t swp_entry; > > - > > - if (write) > > - swp_entry = make_writable_migration_entry( > > - page_to_pfn(page + i)); > > - else if (anon_exclusive) > > - swp_entry = make_readable_exclusive_migration_entry( > > - page_to_pfn(page + i)); > > - else > > - swp_entry = make_readable_migration_entry( > > - page_to_pfn(page + i)); > > - if (young) > > - swp_entry = make_migration_entry_young(swp_entry); > > - if (dirty) > > - swp_entry = make_migration_entry_dirty(swp_entry); > > - entry = swp_entry_to_pte(swp_entry); > > - if (soft_dirty) > > - entry = pte_swp_mksoft_dirty(entry); > > - if (uffd_wp) > > - entry = pte_swp_mkuffd_wp(entry); > > - > > + if (freeze || is_migration_entry(swp_entry)) { > > + if (write) > > + swp_entry = make_writable_migration_entry( > > + page_to_pfn(page + i)); > > + else if (anon_exclusive) > > + swp_entry = make_readable_exclusive_migration_entry( > > + page_to_pfn(page + i)); > > + else > > + swp_entry = make_readable_migration_entry( > > + page_to_pfn(page + i)); > > + if (young) > > + swp_entry = make_migration_entry_young(swp_entry); > > + if (dirty) > > + swp_entry = make_migration_entry_dirty(swp_entry); > > + entry = swp_entry_to_pte(swp_entry); > > + if (soft_dirty) > > + entry = pte_swp_mksoft_dirty(entry); > > + if (uffd_wp) > > + entry = pte_swp_mkuffd_wp(entry); > > + } else { > > + VM_BUG_ON(!is_device_private_entry(swp_entry)); > > + if (write) > > + swp_entry = make_writable_device_private_entry( > > + page_to_pfn(page + i)); > > + else if (anon_exclusive) > > + swp_entry = make_device_exclusive_entry( > > + page_to_pfn(page + i)); > > I am pretty sure this is wrong. You cannot suddenly mix in device-exclusive > entries. > > And now I am confused again how device-private, anon and GUP interact. See my comments on Balbir's v1 resend. I'm pretty sure he's just gotten mixed up with the wonderfully confusing naming I helped create and incorrectly copied the code for making migration entries above. GUP doesn't work for device-private pages - it will fault which will cause the device driver to migrate the pages back. > > + else > > + swp_entry = make_readable_device_private_entry( > > + page_to_pfn(page + i)); > > + entry = swp_entry_to_pte(swp_entry); > > + if (soft_dirty) > > + entry = pte_swp_mksoft_dirty(entry); > > + if (uffd_wp) > > + entry = pte_swp_mkuffd_wp(entry); > > + } > > VM_WARN_ON(!pte_none(ptep_get(pte + i))); > > set_pte_at(mm, addr, pte + i, entry); > > } > > @@ -3065,7 +3105,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, > > } > > pte_unmap(pte); > > - if (!pmd_migration) > > + if (present) > > folio_remove_rmap_pmd(folio, page, vma); > > if (freeze) > > put_page(page); > > @@ -3077,6 +3117,7 @@ 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, struct folio *folio) > > { > > + struct folio *pmd_folio; > > VM_WARN_ON_ONCE(folio && !folio_test_pmd_mappable(folio)); > > VM_WARN_ON_ONCE(!IS_ALIGNED(address, HPAGE_PMD_SIZE)); > > VM_WARN_ON_ONCE(folio && !folio_test_locked(folio)); > > @@ -3089,7 +3130,14 @@ void split_huge_pmd_locked(struct vm_area_struct *vma, unsigned long address, > > */ > > if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd) || > > is_pmd_migration_entry(*pmd)) { > > - if (folio && folio != pmd_folio(*pmd)) > > + if (folio && !pmd_present(*pmd)) { > > + swp_entry_t swp_entry = pmd_to_swp_entry(*pmd); > > + > > + pmd_folio = page_folio(pfn_swap_entry_to_page(swp_entry)); > > + } else { > > + pmd_folio = pmd_folio(*pmd); > > + } > > + if (folio && folio != pmd_folio) > > return; > > __split_huge_pmd_locked(vma, pmd, address, freeze); > > } > > @@ -3581,11 +3629,16 @@ static int __split_unmapped_folio(struct folio *folio, int new_order, > > folio_test_swapcache(origin_folio)) ? > > folio_nr_pages(release) : 0)); > > + if (folio_is_device_private(release)) > > + percpu_ref_get_many(&release->pgmap->ref, > > + (1 << new_order) - 1); > > + > > if (release == origin_folio) > > continue; > > - lru_add_page_tail(origin_folio, &release->page, > > - lruvec, list); > > + if (!folio_is_device_private(origin_folio)) > > + lru_add_page_tail(origin_folio, &release->page, > > + lruvec, list); > > /* Some pages can be beyond EOF: drop them from page cache */ > > if (release->index >= end) { > > @@ -4625,7 +4678,10 @@ int set_pmd_migration_entry(struct page_vma_mapped_walk *pvmw, > > return 0; > > flush_cache_range(vma, address, address + HPAGE_PMD_SIZE); > > - pmdval = pmdp_invalidate(vma, address, pvmw->pmd); > > + if (!folio_is_device_private(folio)) > > + pmdval = pmdp_invalidate(vma, address, pvmw->pmd); > > + else > > + pmdval = pmdp_huge_clear_flush(vma, address, pvmw->pmd); > > Please handle this like we handle the PTE case -- checking for pmd_present() > instead. > > Avoid placing these nasty folio_is_device_private() all over the place where > avoidable. > > > /* See folio_try_share_anon_rmap_pmd(): invalidate PMD first. */ > > anon_exclusive = folio_test_anon(folio) && PageAnonExclusive(page); > > @@ -4675,6 +4731,17 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new) > > entry = pmd_to_swp_entry(*pvmw->pmd); > > folio_get(folio); > > pmde = mk_huge_pmd(new, READ_ONCE(vma->vm_page_prot)); > > + > > + if (unlikely(folio_is_device_private(folio))) { > > + if (pmd_write(pmde)) > > + entry = make_writable_device_private_entry( > > + page_to_pfn(new)); > > + else > > + entry = make_readable_device_private_entry( > > + page_to_pfn(new)); > > + pmde = swp_entry_to_pmd(entry); > > + } > > + > > if (pmd_swp_soft_dirty(*pvmw->pmd)) > > pmde = pmd_mksoft_dirty(pmde); > > if (is_writable_migration_entry(entry)) > > diff --git a/mm/migrate.c b/mm/migrate.c > > index 59e39aaa74e7..0aa1bdb711c3 100644 > > --- a/mm/migrate.c > > +++ b/mm/migrate.c > > @@ -200,6 +200,8 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw, > > if (PageCompound(page)) > > return false; > > + if (folio_is_device_private(folio)) > > + return false; > > Why is that check required when you are adding THP handling and there is a > PageCompound check right there? > > > VM_BUG_ON_PAGE(!PageAnon(page), page); > > VM_BUG_ON_PAGE(!PageLocked(page), page); > > VM_BUG_ON_PAGE(pte_present(*pvmw->pte), page); > > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > > index e463c3be934a..5dd2e51477d3 100644 > > --- a/mm/page_vma_mapped.c > > +++ b/mm/page_vma_mapped.c > > @@ -278,6 +278,16 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > > * cannot return prematurely, while zap_huge_pmd() has > > * cleared *pmd but not decremented compound_mapcount(). > > */ > > + swp_entry_t entry; > > + > > + if (!thp_migration_supported()) > > + return not_found(pvmw); > > This check looks misplaced. We should follow the same model as check_pte(). > > Checking for THP migration support when you are actually caring about > device-private entries is weird. > > That is, I would expect something like > > } else if (is_swap_pmd(pmde)) { > swp_entry_t entry; > > entry = pmd_to_swp_entry(pmde); > if (!is_device_private_entry(entry)) > return false; > > ... > } > > > + entry = pmd_to_swp_entry(pmde); > > + if (is_device_private_entry(entry)) { > > + pvmw->ptl = pmd_lock(mm, pvmw->pmd); > > + return true; > > + } > > + > > if ((pvmw->flags & PVMW_SYNC) && > > thp_vma_suitable_order(vma, pvmw->address, > > PMD_ORDER) && > > diff --git a/mm/rmap.c b/mm/rmap.c > > index 67bb273dfb80..67e99dc5f2ef 100644 > > --- a/mm/rmap.c > > +++ b/mm/rmap.c > > @@ -2326,8 +2326,23 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, > > #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION > > /* PMD-mapped THP migration entry */ > > if (!pvmw.pte) { > > - subpage = folio_page(folio, > > - pmd_pfn(*pvmw.pmd) - folio_pfn(folio)); > > + /* > > + * Zone device private folios do not work well with > > + * pmd_pfn() on some architectures due to pte > > + * inversion. > > + */ > > + if (folio_is_device_private(folio)) { > > + swp_entry_t entry = pmd_to_swp_entry(*pvmw.pmd); > > + unsigned long pfn = swp_offset_pfn(entry); > > + > > + subpage = folio_page(folio, pfn > > + - folio_pfn(folio)); > > + } else { > > + subpage = folio_page(folio, > > + pmd_pfn(*pvmw.pmd) > > + - folio_pfn(folio)); > > + } > > + > > > Please follow the same model we use for PTEs. > > /* > * Handle PFN swap PMDs, such as device-exclusive ones, that > * actually map pages. > */ > if (likely(pmd_present(...))) { > > } > > > -- > Cheers, > > David / dhildenb >