On 2/3/21 2:00 PM, Joao Martins wrote:
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@xxxxxxxxxx>
Signed-off-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
---
mm/gup.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
diff --git a/mm/gup.c b/mm/gup.c
index d68bcb482b11..4f88dcef39f2 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 unsigned int count_ntails(struct page **pages, unsigned long npages)
Silly naming nit: could we please name this function count_pagetails()? count_ntails
is a bit redundant, plus slightly less clear.
+{
+ struct page *head = compound_head(pages[0]);
+ unsigned int ntails;
+
+ for (ntails = 1; ntails < npages; ntails++) {
+ if (compound_head(pages[ntails]) != head)
+ break;
+ }
+
+ return ntails;
+}
+
+static inline void compound_next(unsigned long i, unsigned long npages,
+ struct page **list, struct page **head,
+ unsigned int *ntails)
+{
+ if (i >= npages)
+ return;
+
+ *ntails = count_ntails(list + i, npages - i);
+ *head = compound_head(list[i]);
+}
+
+#define for_each_compound_head(i, list, npages, head, ntails) \
When using macros, which are dangerous in general, you have to worry about
things like name collisions. I really dislike that C has forced this unsafe
pattern upon us, but of course we are stuck with it, for iterator helpers.
Given that we're stuck, you should probably use names such as __i, __list, etc,
in the the above #define. Otherwise you could stomp on existing variables.
+ 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.
thanks,
--
John Hubbard
NVIDIA
