Re: [PATCH V2] mm/gup: folio_split_user_page_pin

[Steven Sistare <steven.sistare@oracle.com>]

On 9/27/2024 11:58 AM, Jason Gunthorpe wrote:
> On Fri, Sep 27, 2024 at 05:44:52PM +0200, David Hildenbrand wrote:
>> /**
>>   * folio_try_add_pins() - add pins to an already-pinned folio
>>   * @folio: the folio to add more pins to
>>   *
>>   * 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_try_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);
>> }
> 
> That looks pretty good to me too

Looks good and passes my tests, I will add this version in V3 of the patch series.

Are you sure you want "try" in the name folio_try_add_pins?  Usually try means
that any failure is transient and a future call may succeed, but the failures in
try_grab_folio look permanent to me (suggesting that is also a misnomer, but at
least it is not exported).

- Steve