Re: [PATCH v9 6/8] block: Switch to pinning pages.

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On 1/24/23 09:01, David Howells wrote:
Add BIO_PAGE_PINNED to indicate that the pages in a bio are pinned
(FOLL_PIN) and that the pin will need removing.

Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
cc: Jens Axboe <axboe@xxxxxxxxx>
cc: Jan Kara <jack@xxxxxxx>
cc: Christoph Hellwig <hch@xxxxxx>
cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
cc: linux-block@xxxxxxxxxxxxxxx
---

Notes:
     ver #9)
      - Only consider pinning in bio_set_cleanup_mode().  Ref'ing pages in
        struct bio is going away.
      - page_put_unpin() is removed; call unpin_user_page() and put_page()
        directly.
      - Use bio_release_page() in __bio_release_pages().
      - BIO_PAGE_PINNED and BIO_PAGE_REFFED can't both be set, so use if-else
        when testing both of them.
ver #8)
      - Move the infrastructure to clean up pinned pages to this patch [hch].
      - Put BIO_PAGE_PINNED before BIO_PAGE_REFFED as the latter should
        probably be removed at some point.  FOLL_PIN can then be renumbered
        first.

  block/bio.c               |  6 +++---
  block/blk.h               | 21 +++++++++++++++++++++
  include/linux/bio.h       |  3 ++-
  include/linux/blk_types.h |  1 +
  4 files changed, 27 insertions(+), 4 deletions(-)

Neatly avoiding any use of FOLL_PIN or FOLL_GET, good. :)

Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>

thanks,
--
John Hubbard
NVIDIA


diff --git a/block/bio.c b/block/bio.c
index 851c23641a0d..fc45aaa97696 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1176,7 +1176,7 @@ void __bio_release_pages(struct bio *bio, bool mark_dirty)
  	bio_for_each_segment_all(bvec, bio, iter_all) {
  		if (mark_dirty && !PageCompound(bvec->bv_page))
  			set_page_dirty_lock(bvec->bv_page);
-		put_page(bvec->bv_page);
+		bio_release_page(bio, bvec->bv_page);
  	}
  }
  EXPORT_SYMBOL_GPL(__bio_release_pages);
@@ -1496,8 +1496,8 @@ void bio_set_pages_dirty(struct bio *bio)
   * the BIO and re-dirty the pages in process context.
   *
   * It is expected that bio_check_pages_dirty() will wholly own the BIO from
- * here on.  It will run one put_page() against each page and will run one
- * bio_put() against the BIO.
+ * here on.  It will unpin each page and will run one bio_put() against the
+ * BIO.
   */
static void bio_dirty_fn(struct work_struct *work);
diff --git a/block/blk.h b/block/blk.h
index 4c3b3325219a..32b252903f9a 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -425,6 +425,27 @@ int bio_add_hw_page(struct request_queue *q, struct bio *bio,
  		struct page *page, unsigned int len, unsigned int offset,
  		unsigned int max_sectors, bool *same_page);
+/*
+ * Set the cleanup mode for a bio from an iterator and the extraction flags.
+ */
+static inline void bio_set_cleanup_mode(struct bio *bio, struct iov_iter *iter)
+{
+	if (iov_iter_extract_will_pin(iter))
+		bio_set_flag(bio, BIO_PAGE_PINNED);
+}
+
+/*
+ * 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)
+{
+	if (bio_flagged(bio, BIO_PAGE_PINNED))
+		unpin_user_page(page);
+	else if (bio_flagged(bio, BIO_PAGE_REFFED))
+		put_page(page);
+}
+
  struct request_queue *blk_alloc_queue(int node_id);
int disk_scan_partitions(struct gendisk *disk, fmode_t mode, void *owner);
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 805957c99147..b2c09997d79c 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -484,7 +484,8 @@ void zero_fill_bio(struct bio *bio);
static inline void bio_release_pages(struct bio *bio, bool mark_dirty)
  {
-	if (bio_flagged(bio, BIO_PAGE_REFFED))
+	if (bio_flagged(bio, BIO_PAGE_REFFED) ||
+	    bio_flagged(bio, BIO_PAGE_PINNED))
  		__bio_release_pages(bio, mark_dirty);
  }
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index 7daa261f4f98..a0e339ff3d09 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -318,6 +318,7 @@ struct bio {
   * bio flags
   */
  enum {
+	BIO_PAGE_PINNED,	/* Unpin pages in bio_release_pages() */
  	BIO_PAGE_REFFED,	/* put pages in bio_release_pages() */
  	BIO_CLONED,		/* doesn't own data */
  	BIO_BOUNCED,		/* bio is a bounce bio */





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