pve-kernel-qoup/patches/kernel/0009-block-add-a-lower-level-bio_add_page-interface.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@lst.de>
Date: Tue, 9 Oct 2018 17:04:39 +0100
Subject: [PATCH] block: add a lower-level bio_add_page interface

Buglink: https://bugs.launchpad.net/bugs/1796542

For the upcoming removal of buffer heads in XFS we need to keep track of
the number of outstanding writeback requests per page.  For this we need
to know if bio_add_page merged a region with the previous bvec or not.
Instead of adding additional arguments this refactors bio_add_page to
be implemented using three lower level helpers which users like XFS can
use directly if they care about the merge decisions.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
(cherry picked from commit 0aa69fd32a5f766e997ca8ab4723c5a1146efa8b)
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
---
 block/bio.c         | 98 ++++++++++++++++++++++++++++++++++-------------------
 include/linux/bio.h |  9 +++++
 2 files changed, 73 insertions(+), 34 deletions(-)

diff --git a/block/bio.c b/block/bio.c
index 4b48f8eefc4c..2636d15af979 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -773,7 +773,7 @@ int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page
 			return 0;
 	}
 
-	if (bio->bi_vcnt >= bio->bi_max_vecs)
+	if (bio_full(bio))
 		return 0;
 
 	/*
@@ -821,6 +821,65 @@ int bio_add_pc_page(struct request_queue *q, struct bio *bio, struct page
 EXPORT_SYMBOL(bio_add_pc_page);
 
 /**
+ * __bio_try_merge_page - try appending data to an existing bvec.
+ * @bio: destination bio
+ * @page: page to add
+ * @len: length of the data to add
+ * @off: offset of the data in @page
+ *
+ * Try to add the data at @page + @off to the last bvec of @bio.  This is a
+ * a useful optimisation for file systems with a block size smaller than the
+ * page size.
+ *
+ * Return %true on success or %false on failure.
+ */
+bool __bio_try_merge_page(struct bio *bio, struct page *page,
+		unsigned int len, unsigned int off)
+{
+	if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
+		return false;
+
+	if (bio->bi_vcnt > 0) {
+		struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
+
+		if (page == bv->bv_page && off == bv->bv_offset + bv->bv_len) {
+			bv->bv_len += len;
+			bio->bi_iter.bi_size += len;
+			return true;
+		}
+	}
+	return false;
+}
+EXPORT_SYMBOL_GPL(__bio_try_merge_page);
+
+/**
+ * __bio_add_page - add page to a bio in a new segment
+ * @bio: destination bio
+ * @page: page to add
+ * @len: length of the data to add
+ * @off: offset of the data in @page
+ *
+ * Add the data at @page + @off to @bio as a new bvec.  The caller must ensure
+ * that @bio has space for another bvec.
+ */
+void __bio_add_page(struct bio *bio, struct page *page,
+		unsigned int len, unsigned int off)
+{
+	struct bio_vec *bv = &bio->bi_io_vec[bio->bi_vcnt];
+
+	WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED));
+	WARN_ON_ONCE(bio_full(bio));
+
+	bv->bv_page = page;
+	bv->bv_offset = off;
+	bv->bv_len = len;
+
+	bio->bi_iter.bi_size += len;
+	bio->bi_vcnt++;
+}
+EXPORT_SYMBOL_GPL(__bio_add_page);
+
+/**
  *	bio_add_page	-	attempt to add page to bio
  *	@bio: destination bio
  *	@page: page to add
@@ -833,40 +892,11 @@ EXPORT_SYMBOL(bio_add_pc_page);
 int bio_add_page(struct bio *bio, struct page *page,
 		 unsigned int len, unsigned int offset)
 {
-	struct bio_vec *bv;
-
-	/*
-	 * cloned bio must not modify vec list
-	 */
-	if (WARN_ON_ONCE(bio_flagged(bio, BIO_CLONED)))
-		return 0;
-
-	/*
-	 * For filesystems with a blocksize smaller than the pagesize
-	 * we will often be called with the same page as last time and
-	 * a consecutive offset.  Optimize this special case.
-	 */
-	if (bio->bi_vcnt > 0) {
-		bv = &bio->bi_io_vec[bio->bi_vcnt - 1];
-
-		if (page == bv->bv_page &&
-		    offset == bv->bv_offset + bv->bv_len) {
-			bv->bv_len += len;
-			goto done;
-		}
+	if (!__bio_try_merge_page(bio, page, len, offset)) {
+		if (bio_full(bio))
+			return 0;
+		__bio_add_page(bio, page, len, offset);
 	}
-
-	if (bio->bi_vcnt >= bio->bi_max_vecs)
-		return 0;
-
-	bv		= &bio->bi_io_vec[bio->bi_vcnt];
-	bv->bv_page	= page;
-	bv->bv_len	= len;
-	bv->bv_offset	= offset;
-
-	bio->bi_vcnt++;
-done:
-	bio->bi_iter.bi_size += len;
 	return len;
 }
 EXPORT_SYMBOL(bio_add_page);
diff --git a/include/linux/bio.h b/include/linux/bio.h
index a98c6ac575cf..3440870712d4 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -123,6 +123,11 @@ static inline void *bio_data(struct bio *bio)
 	return NULL;
 }
 
+static inline bool bio_full(struct bio *bio)
+{
+	return bio->bi_vcnt >= bio->bi_max_vecs;
+}
+
 /*
  * will die
  */
@@ -447,6 +452,10 @@ void bio_chain(struct bio *, struct bio *);
 extern int bio_add_page(struct bio *, struct page *, unsigned int,unsigned int);
 extern int bio_add_pc_page(struct request_queue *, struct bio *, struct page *,
 			   unsigned int, unsigned int);
+bool __bio_try_merge_page(struct bio *bio, struct page *page,
+		unsigned int len, unsigned int off);
+void __bio_add_page(struct bio *bio, struct page *page,
+		unsigned int len, unsigned int off);
 int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter);
 struct rq_map_data;
 extern struct bio *bio_map_user_iov(struct request_queue *,