Re: [PATCH v8 07/10] block: Switch to pinning pages.

[David Howells]

Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:

> It can't.  Per your latest branch:

Yes it can.  Patch 6:

--- a/block/blk-map.c
+++ b/block/blk-map.c
@@ -282,6 +282,7 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
 	if (blk_queue_pci_p2pdma(rq->q))
 		extract_flags |= ITER_ALLOW_P2PDMA;
 
+	bio_set_flag(bio, BIO_PAGE_REFFED);
 	while (iov_iter_count(iter)) {
 		struct page **pages, *stack_pages[UIO_FASTIOV];
 		ssize_t bytes;

Patch 7:

+static inline unsigned int bio_to_gup_flags(struct bio *bio)
+{
+	return (bio_flagged(bio, BIO_PAGE_REFFED) ? FOLL_GET : 0) |
+		(bio_flagged(bio, BIO_PAGE_PINNED) ? FOLL_PIN : 0);
+}
+
+/*
+ * Clean up a page appropriately, where the page may be pinned, may have a
+ * ref taken on it or neither.
+ */
+static inline void bio_release_page(struct bio *bio, struct page *page)
+{
+	page_put_unpin(page, bio_to_gup_flags(bio));
+}

At patch 8, you can get either FOLL_GET, FOLL_PIN or 0, depending on the path
you go through.

David