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mm/gup: Add folio_add_pins()

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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).

Link: https://patch.msgid.link/r/1729861919-234514-2-git-send-email-steven.sistare@oracle.com
Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
This commit is contained in:
Steve Sistare 2024-10-25 06:11:51 -07:00 committed by Jason Gunthorpe
parent e2d8fe9148
commit a2ad1b8101
2 changed files with 25 additions and 0 deletions
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1
include/linux/mm.h
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@ -2524,6 +2524,7 @@ 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);

24
mm/gup.c
View File

@ -3717,3 +3717,27 @@ err:
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);