On 2/4/21 12:24 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.
Given that we won't be iterating on a list of changes, change
compound_next() to receive a bool, whether to calculate from the starting
Thankfully, that claim is stale and can now be removed from this commit
description.
page, or walk the page array. Finally add a separate iterator,
for_each_compound_range() that just operate 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 | 64 ++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 66 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 5a3dd235017a..3426736a01b2 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -215,6 +215,34 @@ void unpin_user_page(struct page *page)
}
EXPORT_SYMBOL(unpin_user_page);
+static inline void range_next(unsigned long i, unsigned long npages,
+ struct page **list, struct page **head,
+ unsigned int *ntails)
Would compound_range_next() be a better name?
+{
+ struct page *next, *page;
+ unsigned int nr = 1;
+
+ if (i >= npages)
+ return;
+
+ npages -= i;
+ 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);
This pointer arithmetic will involve division. Which may be unnecessarily
expensive, if there is a way to calculate this with indices instead of
pointer arithmetic. I'm not sure if there is, off hand, but thought it
worth mentioning because the point is sometimes overlooked.
+
+ *head = page;
+ *ntails = nr;
+}
+
+#define for_each_compound_range(__i, __list, __npages, __head, __ntails) \
+ for (__i = 0, \
+ range_next(__i, __npages, __list, &(__head), &(__ntails)); \
+ __i < __npages; __i += __ntails, \
+ 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)
@@ -306,6 +334,42 @@ 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.
Didn't spot any actual problems with how this works.
thanks,
--
John Hubbard
NVIDIA
