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Message-ID: <f7abedaf-abf0-49aa-b152-31250f2ba7ba@nvidia.com>
Date: Tue, 8 Jul 2025 16:47:35 +1000
From: Balbir Singh <balbirs@...dia.com>
To: Alistair Popple <apopple@...dia.com>
Cc: linux-mm@...ck.org, akpm@...ux-foundation.org,
linux-kernel@...r.kernel.org, Karol Herbst <kherbst@...hat.com>,
Lyude Paul <lyude@...hat.com>, Danilo Krummrich <dakr@...nel.org>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
Jérôme Glisse <jglisse@...hat.com>,
Shuah Khan <shuah@...nel.org>, David Hildenbrand <david@...hat.com>,
Barry Song <baohua@...nel.org>, Baolin Wang <baolin.wang@...ux.alibaba.com>,
Ryan Roberts <ryan.roberts@....com>, Matthew Wilcox <willy@...radead.org>,
Peter Xu <peterx@...hat.com>, Zi Yan <ziy@...dia.com>,
Kefeng Wang <wangkefeng.wang@...wei.com>, Jane Chu <jane.chu@...cle.com>,
Donet Tom <donettom@...ux.ibm.com>
Subject: Re: [v1 resend 01/12] mm/zone_device: support large zone device
private folios
On 7/7/25 15:28, Alistair Popple wrote:
> On Fri, Jul 04, 2025 at 09:35:00AM +1000, Balbir Singh wrote:
>> Add routines to support allocation of large order zone device folios
>> and helper functions for zone device folios, to check if a folio is
>> device private and helpers for setting zone device data.
>>
>> When large folios are used, the existing page_free() callback in
>> pgmap is called when the folio is freed, this is true for both
>> PAGE_SIZE and higher order pages.
>>
>> Cc: Karol Herbst <kherbst@...hat.com>
>> Cc: Lyude Paul <lyude@...hat.com>
>> Cc: Danilo Krummrich <dakr@...nel.org>
>> Cc: David Airlie <airlied@...il.com>
>> Cc: Simona Vetter <simona@...ll.ch>
>> Cc: "Jérôme Glisse" <jglisse@...hat.com>
>> Cc: Shuah Khan <shuah@...nel.org>
>> Cc: David Hildenbrand <david@...hat.com>
>> Cc: Barry Song <baohua@...nel.org>
>> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
>> Cc: Ryan Roberts <ryan.roberts@....com>
>> Cc: Matthew Wilcox <willy@...radead.org>
>> Cc: Peter Xu <peterx@...hat.com>
>> Cc: Zi Yan <ziy@...dia.com>
>> Cc: Kefeng Wang <wangkefeng.wang@...wei.com>
>> Cc: Jane Chu <jane.chu@...cle.com>
>> Cc: Alistair Popple <apopple@...dia.com>
>> Cc: Donet Tom <donettom@...ux.ibm.com>
>>
>> Signed-off-by: Balbir Singh <balbirs@...dia.com>
>> ---
>> include/linux/memremap.h | 22 +++++++++++++++++-
>> mm/memremap.c | 50 +++++++++++++++++++++++++++++-----------
>> 2 files changed, 58 insertions(+), 14 deletions(-)
>>
>> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
>> index 4aa151914eab..11d586dd8ef1 100644
>> --- a/include/linux/memremap.h
>> +++ b/include/linux/memremap.h
>> @@ -169,6 +169,18 @@ static inline bool folio_is_device_private(const struct folio *folio)
>> return is_device_private_page(&folio->page);
>> }
>>
>> +static inline void *folio_zone_device_data(const struct folio *folio)
>> +{
>> + VM_BUG_ON_FOLIO(!folio_is_device_private(folio), folio);
>> + return folio->page.zone_device_data;
>> +}
>> +
>> +static inline void folio_set_zone_device_data(struct folio *folio, void *data)
>> +{
>> + VM_BUG_ON_FOLIO(!folio_is_device_private(folio), folio);
>> + folio->page.zone_device_data = data;
>> +}
>> +
>> static inline bool is_pci_p2pdma_page(const struct page *page)
>> {
>> return IS_ENABLED(CONFIG_PCI_P2PDMA) &&
>> @@ -199,7 +211,7 @@ static inline bool folio_is_fsdax(const struct folio *folio)
>> }
>>
>> #ifdef CONFIG_ZONE_DEVICE
>> -void zone_device_page_init(struct page *page);
>> +void init_zone_device_folio(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 +221,14 @@ 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);
>> +
>> + init_zone_device_folio(folio, 0);
>
> Minor nit, but why not call this zone_device_folio_init() to keep the naming
> consistent with zone_device_page_init()?
>
Ack, will do!
>> +}
>> +
>> #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..4085a3893e64 100644
>> --- a/mm/memremap.c
>> +++ b/mm/memremap.c
>> @@ -427,20 +427,21 @@ 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;
>> + bool anon = folio_test_anon(folio);
>> + struct page *page = folio_page(folio, 0);
>>
>> 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));
>> + WARN_ON_ONCE(folio_test_large(folio) && !anon);
>> +
>> + for (i = 0; i < nr; i++) {
>
> The above comment says we should do this for all tail pages, but this appears to
> do it for the head page as well. Is there a particular reason for that?
>
The original code clears the head page (when the folio is not large), the only
page. I don't think the head page can be skipped.
>> + if (anon)
>> + __ClearPageAnonExclusive(folio_page(folio, i));
>> }
>>
>> /*
>> @@ -464,10 +465,19 @@ void free_zone_device_folio(struct folio *folio)
>>
>> switch (pgmap->type) {
>> case MEMORY_DEVICE_PRIVATE:
>> + if (folio_test_large(folio)) {
>> + folio_unqueue_deferred_split(folio);
>> +
>> + percpu_ref_put_many(&folio->pgmap->ref, nr - 1);
>> + }
>> + pgmap->ops->page_free(page);
>> + put_dev_pagemap(pgmap);
>
> Why is this needed/added, and where is the associated get_dev_pagemap()? Note
> that the whole {get|put}_dev_pagemap() thing is basically unused now. Which
> reminds me I should send a patch to remove it.
>
Thanks, I'll remove these bits
>> + 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));
>> + pgmap->ops->page_free(page);
>> put_dev_pagemap(pgmap);
>> break;
>>
>> @@ -491,14 +501,28 @@ void free_zone_device_folio(struct folio *folio)
>> }
>> }
>>
>> -void zone_device_page_init(struct page *page)
>> +void init_zone_device_folio(struct folio *folio, unsigned int order)
>
> See above for some bike-shedding on the name.
>
Ack
>> {
>> + struct page *page = folio_page(folio, 0);
>> +
>> + VM_BUG_ON(order > MAX_ORDER_NR_PAGES);
>> +
>> + 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);
>> +
>> + /*
>> + * Only PMD level migration is supported for THP migration
>> + */
>> + if (order > 1) {
>> + prep_compound_page(page, order);
>
> Shouldn't this happen for order > 0 not 1? What about calling
> INIT_LIST_HEAD(&folio->_deferred_list)? Last time I looked prep_compound_page()
> didn't do that and I see above you are calling folio_unqueue_deferred_split() so
> I assume you need to do this for DEVICE_PRIVATE pages too.
>
order == 1 has no deferred_list. prep_compound_page handles the INIT_LIST_HEAD
>> + folio_set_large_rmappable(folio);
>> + }
>> }
>> -EXPORT_SYMBOL_GPL(zone_device_page_init);
>> +EXPORT_SYMBOL_GPL(init_zone_device_folio);
>> --
>> 2.49.0
>>
Thanks for the review
Balbir
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