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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 18.09.24 16:51, Steven Sistare wrote: > On 9/17/2024 8:25 AM, David Hildenbrand wrote: >> On 14.09.24 15:19, Steven Sistare wrote: >>> cc'ing linux-mm for review of this one patch of the series. >>> >>> This proposes a new KAPI function repin_folio_unhugely(), for use in this >>> patch of the iommu_ioas_map_file series: >>> >>>     iommufd: IOMMU_IOAS_MAP_FILE implementation >>>     https://lore.kernel.org/linux-iommu/1726319158-283074-7-git-send-email-steven.sistare@oracle.com >>> >>> - Steve >>> >>> On 9/14/2024 9:05 AM, Steve Sistare wrote: >>>> Export a function that repins a huge-page folio at small-page granularity. >>>> 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 >>>> repin_folio_unhugely could be unpinned via unpin_user_page(s). >>>> >>>> Suggested-by: Jason Gunthorpe >>>> Signed-off-by: Steve Sistare >>>> --- >>>>    include/linux/mm.h |  1 + >>>>    mm/gup.c           | 18 ++++++++++++++++++ >>>>    2 files changed, 19 insertions(+) >>>> >>>> diff --git a/include/linux/mm.h b/include/linux/mm.h >>>> index 1470736..ba8344f 100644 >>>> --- a/include/linux/mm.h >>>> +++ b/include/linux/mm.h >>>> @@ -2514,6 +2514,7 @@ 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); >>>> +void repin_folio_unhugely(struct folio *folio, unsigned long npin); >>>>    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 947881ff..f8f3f2a 100644 >>>> --- a/mm/gup.c >>>> +++ b/mm/gup.c >>>> @@ -3720,3 +3720,21 @@ long memfd_pin_folios(struct file *memfd, loff_t start, loff_t end, >>>>        return ret; >>>>    } >>>>    EXPORT_SYMBOL_GPL(memfd_pin_folios); >>>> + >>>> +/** >>>> + * repin_folio_unhugely() - repin a folio at small page granularity >>>> + * @folio: the folio to repin >>>> + * @npin:  the number of pages pinned in the folio >>>> + * >>>> + * Given a huge page folio that is already pinned, and the number of small >> >> s/huge page folio/large folio/ >> >>>> + * pages that are pinned in it, adjust the pincount to reflect small-page >>>> + * granularity.  Each small page can later be unpinned individually. >>>> + */ >>>> +void repin_folio_unhugely(struct folio *folio, unsigned long npin) >>>> +{ >>>> +    if (!folio_test_large(folio) || is_huge_zero_folio(folio) || npin == 1) >> >> Why not the huge zero folio? That looks very odd here. > > The zero page is treated specially here and elsewhere, it can never be deleted so > reference fiddling is skipped. Please point me in mm/gup.c at that handling. IIRC is_zero_folio() does *not* include the huge zero page. Yes, we should likely be special-casing the huge zeropage in mm/gup.c, but it's not that easy because PINs can outlive MMs ... so *not* grabbing a reference could currently be harmful. But that has do be changed consistently, not with doing things here different compared to other gup.c functions. > >>>> +        return; >>>> +    atomic_add(npin - 1, &folio->_refcount); >>>> +    atomic_add(npin - 1, &folio->_pincount); >>>> +} >>>> +EXPORT_SYMBOL_GPL(repin_folio_unhugely); >> >> Can we ... find a better name? For example, it's "large" folio not "huge"... >> >> And repin is really misleading. We are simply adding more pins to an already pinned one ... > > Jason suggests a better name in the other thread. I would prefer something that simply adds more pins to an already pinned folio. Much easier to get. -- Cheers, David / dhildenb