mm: release number of pages of a folio

Add a new function unpin_user_folio() to put the refs of a folio by
npages count.

The check for BIO_PAGE_PINNED flag is removed as it is already checked
in bio_release_pages().

Signed-off-by: Kundan Kumar <kundan.kumar@samsung.com>
Tested-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20240911064935.5630-4-kundan.kumar@samsung.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/mm.h

@@ -1597,6 +1597,7 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
 void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
 				      bool make_dirty);
 void unpin_user_pages(struct page **pages, unsigned long npages);
+void unpin_user_folio(struct folio *folio, unsigned long npages);
 void unpin_folios(struct folio **folios, unsigned long nfolios);
 
 static inline bool is_cow_mapping(vm_flags_t flags)

mm/gup.c

@@ -415,6 +415,19 @@ void unpin_user_pages(struct page **pages, unsigned long npages)
 }
 EXPORT_SYMBOL(unpin_user_pages);
 
+/**
+ * unpin_user_folio() - release pages of a folio
+ * @folio:  pointer to folio to be released
+ * @npages: number of pages of same folio
+ *
+ * Release npages of the folio
+ */
+void unpin_user_folio(struct folio *folio, unsigned long npages)
+{
+	gup_put_folio(folio, npages, FOLL_PIN);
+}
+EXPORT_SYMBOL(unpin_user_folio);
+
 /**
  * unpin_folios() - release an array of gup-pinned folios.
  * @folios:  array of folios to be marked dirty and released.