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>> +void zone_device_folio_init(struct folio *folio, unsigned int order); >>   void *memremap_pages(struct dev_pagemap *pgmap, int nid); >>   void memunmap_pages(struct dev_pagemap *pgmap); >>   void *devm_memremap_pages(struct device *dev, struct dev_pagemap *pgmap); >> @@ -209,6 +209,14 @@ struct dev_pagemap *get_dev_pagemap(unsigned long pfn, >>   bool pgmap_pfn_valid(struct dev_pagemap *pgmap, unsigned long pfn); >>     unsigned long memremap_compat_align(void); >> + >> +static inline void zone_device_page_init(struct page *page) >> +{ >> +    struct folio *folio = page_folio(page); >> + >> +    zone_device_folio_init(folio, 0); >> +} >> + >>   #else >>   static inline void *devm_memremap_pages(struct device *dev, >>           struct dev_pagemap *pgmap) >> diff --git a/mm/memremap.c b/mm/memremap.c >> index b0ce0d8254bd..3ca136e7455e 100644 >> --- a/mm/memremap.c >> +++ b/mm/memremap.c >> @@ -427,20 +427,19 @@ EXPORT_SYMBOL_GPL(get_dev_pagemap); >>   void free_zone_device_folio(struct folio *folio) >>   { >>       struct dev_pagemap *pgmap = folio->pgmap; >> +    unsigned int nr = folio_nr_pages(folio); >> +    int i; > > "unsigned long" is to be future-proof. Will change this for v3 > > (folio_nr_pages() returns long and probably soon unsigned long) > > [ I'd probably all it "nr_pages" ] Ack > >>         if (WARN_ON_ONCE(!pgmap)) >>           return; >>         mem_cgroup_uncharge(folio); >>   -    /* >> -     * Note: we don't expect anonymous compound pages yet. Once supported >> -     * and we could PTE-map them similar to THP, we'd have to clear >> -     * PG_anon_exclusive on all tail pages. >> -     */ >>       if (folio_test_anon(folio)) { >> -        VM_BUG_ON_FOLIO(folio_test_large(folio), folio); >> -        __ClearPageAnonExclusive(folio_page(folio, 0)); >> +        for (i = 0; i < nr; i++) >> +            __ClearPageAnonExclusive(folio_page(folio, i)); >> +    } else { >> +        VM_WARN_ON_ONCE(folio_test_large(folio)); >>       } >>         /* >> @@ -464,11 +463,20 @@ void free_zone_device_folio(struct folio *folio) >>         switch (pgmap->type) { >>       case MEMORY_DEVICE_PRIVATE: >> +        if (folio_test_large(folio)) { > > Could do "nr > 1" if we already have that value around. > Ack >> +            folio_unqueue_deferred_split(folio); > > I think I asked that already but maybe missed the reply: Should these folios ever be added to the deferred split queue and is there any value in splitting them under memory pressure in the shrinker? > > My gut feeling is "No", because the buddy cannot make use of these folios, but maybe there is an interesting case where we want that behavior? > >> + >> +            percpu_ref_put_many(&folio->pgmap->ref, nr - 1); >> +        } >> +        pgmap->ops->page_free(&folio->page); >> +        percpu_ref_put(&folio->pgmap->ref); > > Coold you simply do a > >     percpu_ref_put_many(&folio->pgmap->ref, nr); > > here, or would that be problematic? > I can definitely try that >> +        folio->page.mapping = NULL; >> +        break; >>       case MEMORY_DEVICE_COHERENT: >>           if (WARN_ON_ONCE(!pgmap->ops || !pgmap->ops->page_free)) >>               break; >> -        pgmap->ops->page_free(folio_page(folio, 0)); >> -        put_dev_pagemap(pgmap); >> +        pgmap->ops->page_free(&folio->page); >> +        percpu_ref_put(&folio->pgmap->ref); >>           break; >>         case MEMORY_DEVICE_GENERIC: >> @@ -491,14 +499,28 @@ void free_zone_device_folio(struct folio *folio) >>       } >>   } >>   -void zone_device_page_init(struct page *page) >> +void zone_device_folio_init(struct folio *folio, unsigned int order) >>   { >> +    struct page *page = folio_page(folio, 0); >> + >> +    VM_WARN_ON_ONCE(order > MAX_ORDER_NR_PAGES); >> + >> +    /* >> +     * Only PMD level migration is supported for THP migration >> +     */ > > Talking about something that does not exist yet (and is very specific) sounds a bit weird. > > Should this go into a different patch, or could we rephrase the comment to be a bit more generic? > > In this patch here, nothing would really object to "order" being intermediate. > > (also, this is a device_private limitation? shouldn't that check go somehwere where we can perform this device-private limitation check?) > I can remove the limitation and keep it generic >> +    WARN_ON_ONCE(order && order != HPAGE_PMD_ORDER); >> + >>       /* >>        * Drivers shouldn't be allocating pages after calling >>        * memunmap_pages(). >>        */ >> -    WARN_ON_ONCE(!percpu_ref_tryget_live(&page_pgmap(page)->ref)); >> -    set_page_count(page, 1); >> +    WARN_ON_ONCE(!percpu_ref_tryget_many(&page_pgmap(page)->ref, 1 << order)); >> +    folio_set_count(folio, 1); >>       lock_page(page); >> + >> +    if (order > 1) { >> +        prep_compound_page(page, order); >> +        folio_set_large_rmappable(folio); >> +    } >>   } >> -EXPORT_SYMBOL_GPL(zone_device_page_init); >> +EXPORT_SYMBOL_GPL(zone_device_folio_init); > > Thanks, Balbir