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Subject[PATCH v2 1/4] mm/gup: add compound page list iterator
Date
Add an helper that iterates over head pages in a list of pages. It
essentially counts the tails until the next page to process has a
different head that the current. This is going to be used by
unpin_user_pages() family of functions, to batch the head page refcount
updates once for all passed consecutive tail pages.

Suggested-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
---
mm/gup.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index d68bcb482b11..d1549c61c2f6 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -215,6 +215,35 @@ void unpin_user_page(struct page *page)
}
EXPORT_SYMBOL(unpin_user_page);

+static inline void compound_next(unsigned long i, unsigned long npages,
+ struct page **list, struct page **head,
+ unsigned int *ntails)
+{
+ struct page *page;
+ unsigned int nr;
+
+ if (i >= npages)
+ return;
+
+ list += i;
+ npages -= i;
+ page = compound_head(*list);
+
+ for (nr = 1; nr < npages; nr++) {
+ if (compound_head(list[nr]) != page)
+ break;
+ }
+
+ *head = page;
+ *ntails = nr;
+}
+
+#define for_each_compound_head(__i, __list, __npages, __head, __ntails) \
+ for (__i = 0, \
+ compound_next(__i, __npages, __list, &(__head), &(__ntails)); \
+ __i < __npages; __i += __ntails, \
+ compound_next(__i, __npages, __list, &(__head), &(__ntails)))
+
/**
* unpin_user_pages_dirty_lock() - release and optionally dirty gup-pinned pages
* @pages: array of pages to be maybe marked dirty, and definitely released.
--
2.17.1
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