Re: [PATCH v3 3/4] mm/gup: add a range variant of unpin_user_pages_dirty_lock()

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On 2/5/21 12:41 PM, Joao Martins wrote:
Add a unpin_user_page_range_dirty_lock() API which takes a starting page
and how many consecutive pages we want to unpin and optionally dirty.

To that end, define another iterator for_each_compound_range()
that operates in page ranges as opposed to page array.

For users (like RDMA mr_dereg) where each sg represents a
contiguous set of pages, we're able to more efficiently unpin
pages without having to supply an array of pages much of what
happens today with unpin_user_pages().

Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Joao Martins <joao.m.martins@xxxxxxxxxx>
---
  include/linux/mm.h |  2 ++
  mm/gup.c           | 62 ++++++++++++++++++++++++++++++++++++++++++++++
  2 files changed, 64 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a608feb0d42e..b76063f7f18a 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1265,6 +1265,8 @@ static inline void put_page(struct page *page)
  void unpin_user_page(struct page *page);
  void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
  				 bool make_dirty);
+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);
/**
diff --git a/mm/gup.c b/mm/gup.c
index 467a11df216d..938964d31494 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -215,6 +215,32 @@ void unpin_user_page(struct page *page)
  }
  EXPORT_SYMBOL(unpin_user_page);
+static inline void compound_range_next(unsigned long i, unsigned long npages,
+				       struct page **list, struct page **head,
+				       unsigned int *ntails)

Yes, the new names look good, and I have failed to find any logic errors, so:

Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>

thanks,
--
John Hubbard
NVIDIA

+{
+	struct page *next, *page;
+	unsigned int nr = 1;
+
+	if (i >= npages)
+		return;
+
+	next = *list + i;
+	page = compound_head(next);
+	if (PageCompound(page) && compound_order(page) >= 1)
+		nr = min_t(unsigned int,
+			   page + compound_nr(page) - next, npages - i);
+
+	*head = page;
+	*ntails = nr;
+}
+
+#define for_each_compound_range(__i, __list, __npages, __head, __ntails) \
+	for (__i = 0, \
+	     compound_range_next(__i, __npages, __list, &(__head), &(__ntails)); \
+	     __i < __npages; __i += __ntails, \
+	     compound_range_next(__i, __npages, __list, &(__head), &(__ntails)))
+
  static inline void compound_next(unsigned long i, unsigned long npages,
  				 struct page **list, struct page **head,
  				 unsigned int *ntails)
@@ -303,6 +329,42 @@ void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages,
  }
  EXPORT_SYMBOL(unpin_user_pages_dirty_lock);
+/**
+ * unpin_user_page_range_dirty_lock() - release and optionally dirty
+ * gup-pinned page range
+ *
+ * @page:  the starting page of a range maybe marked dirty, and definitely released.
+ * @npages: number of consecutive pages to release.
+ * @make_dirty: whether to mark the pages dirty
+ *
+ * "gup-pinned page range" refers to a range of pages that has had one of the
+ * get_user_pages() variants called on that page.
+ *
+ * For the page ranges defined by [page .. page+npages], make that range (or
+ * its head pages, if a compound page) dirty, if @make_dirty is true, and if the
+ * page range was previously listed as clean.
+ *
+ * set_page_dirty_lock() is used internally. If instead, set_page_dirty() is
+ * required, then the caller should a) verify that this is really correct,
+ * because _lock() is usually required, and b) hand code it:
+ * set_page_dirty_lock(), unpin_user_page().
+ *
+ */
+void unpin_user_page_range_dirty_lock(struct page *page, unsigned long npages,
+				      bool make_dirty)
+{
+	unsigned long index;
+	struct page *head;
+	unsigned int ntails;
+
+	for_each_compound_range(index, &page, npages, head, ntails) {
+		if (make_dirty && !PageDirty(head))
+			set_page_dirty_lock(head);
+		put_compound_head(head, ntails, FOLL_PIN);
+	}
+}
+EXPORT_SYMBOL(unpin_user_page_range_dirty_lock);
+
  /**
   * unpin_user_pages() - release an array of gup-pinned pages.
   * @pages:  array of pages to be marked dirty and released.





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