Re: [PATCH V3 1/9] mm/gup: folio_add_pins

[David Hildenbrand <david@redhat.com>]

On 04.10.24 20:52, Steven Sistare wrote:
> cc mm folks.
> 
> On 10/4/2024 2:48 PM, Steve Sistare wrote:
>> Export a function that adds pins to an already-pinned huge-page folio.
>> This allows any range of small pages within the folio to be unpinned later.
>> For example, pages pinned via memfd_pin_folios and modified by
>> folio_add_pins could be unpinned via unpin_user_page(s).
>>
>> Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
>> Suggested-by: David Hildenbrand <david@redhat.com>
>> Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
>> ---
>>    include/linux/mm.h |  1 +
>>    mm/gup.c           | 24 ++++++++++++++++++++++++
>>    2 files changed, 25 insertions(+)
>>
>> diff --git a/include/linux/mm.h b/include/linux/mm.h
>> index 13bff7c..70d5293 100644
>> --- a/include/linux/mm.h
>> +++ b/include/linux/mm.h
>> @@ -2521,6 +2521,7 @@ long pin_user_pages_unlocked(unsigned long start, unsigned long nr_pages,
>>    long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end,
>>    		      struct folio **folios, unsigned int max_folios,
>>    		      pgoff_t *offset);
>> +int folio_add_pins(struct folio *folio, unsigned int pins);
>>    
>>    int get_user_pages_fast(unsigned long start, int nr_pages,
>>    			unsigned int gup_flags, struct page **pages);
>> diff --git a/mm/gup.c b/mm/gup.c
>> index fcd602b..11c5f27 100644
>> --- a/mm/gup.c
>> +++ b/mm/gup.c
>> @@ -3733,3 +3733,27 @@ long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end,
>>    	return ret;
>>    }
>>    EXPORT_SYMBOL_GPL(memfd_pin_folios);
>> +
>> +/**
>> + * folio_add_pins() - add pins to an already-pinned folio
>> + * @folio: the folio to add more pins to
>> + * @pins: number of pins to add
>> + *
>> + * Try to add more pins to an already-pinned folio. The semantics
>> + * of the pin (e.g., FOLL_WRITE) follow any existing pin and cannot
>> + * be changed.
>> + *
>> + * This function is helpful when having obtained a pin on a large folio
>> + * using memfd_pin_folios(), but wanting to logically unpin parts
>> + * (e.g., individual pages) of the folio later, for example, using
>> + * unpin_user_page_range_dirty_lock().
>> + *
>> + * This is not the right interface to initially pin a folio.
>> + */
>> +int folio_add_pins(struct folio *folio, unsigned int pins)
>> +{
>> +	VM_WARN_ON_ONCE(!folio_maybe_dma_pinned(folio));
>> +
>> +	return try_grab_folio(folio, pins, FOLL_PIN);
>> +}
>> +EXPORT_SYMBOL_GPL(folio_add_pins);
> 


Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb