block: Remove forced page bouncing under IO

JBD layer wrote back data buffers without setting PageWriteback bit.
Thus standard mechanism for guaranteeing stable pages under IO did not
work. Since JBD is gone now and there is no other user of the
functionality, just remove it.
Acked-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NJan Kara <jack@suse.cz>

block/bounce.c

@@ -176,26 +176,8 @@ static void bounce_end_io_read_isa(struct bio *bio, int err)
 	__bounce_end_io_read(bio, isa_page_pool, err);
 }
 
-#ifdef CONFIG_NEED_BOUNCE_POOL
-static int must_snapshot_stable_pages(struct request_queue *q, struct bio *bio)
-{
-	if (bio_data_dir(bio) != WRITE)
-		return 0;
-
-	if (!bdi_cap_stable_pages_required(&q->backing_dev_info))
-		return 0;
-
-	return test_bit(BIO_SNAP_STABLE, &bio->bi_flags);
-}
-#else
-static int must_snapshot_stable_pages(struct request_queue *q, struct bio *bio)
-{
-	return 0;
-}
-#endif /* CONFIG_NEED_BOUNCE_POOL */
-
 static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
-			       mempool_t *pool, int force)
+			       mempool_t *pool)
 {
 	struct bio *bio;
 	int rw = bio_data_dir(*bio_orig);
@@ -203,8 +185,6 @@ static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
 	struct bvec_iter iter;
 	unsigned i;
 
-	if (force)
-		goto bounce;
 	bio_for_each_segment(from, *bio_orig, iter)
 		if (page_to_pfn(from.bv_page) > queue_bounce_pfn(q))
 			goto bounce;
@@ -216,7 +196,7 @@ static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
 	bio_for_each_segment_all(to, bio, i) {
 		struct page *page = to->bv_page;
 
-		if (page_to_pfn(page) <= queue_bounce_pfn(q) && !force)
+		if (page_to_pfn(page) <= queue_bounce_pfn(q))
 			continue;
 
 		to->bv_page = mempool_alloc(pool, q->bounce_gfp);
@@ -254,7 +234,6 @@ static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
 
 void blk_queue_bounce(struct request_queue *q, struct bio **bio_orig)
 {
-	int must_bounce;
 	mempool_t *pool;
 
 	/*
@@ -263,15 +242,13 @@ void blk_queue_bounce(struct request_queue *q, struct bio **bio_orig)
 	if (!bio_has_data(*bio_orig))
 		return;
 
-	must_bounce = must_snapshot_stable_pages(q, *bio_orig);
-
 	/*
 	 * for non-isa bounce case, just check if the bounce pfn is equal
 	 * to or bigger than the highest pfn in the system -- in that case,
 	 * don't waste time iterating over bio segments
 	 */
 	if (!(q->bounce_gfp & GFP_DMA)) {
-		if (queue_bounce_pfn(q) >= blk_max_pfn && !must_bounce)
+		if (queue_bounce_pfn(q) >= blk_max_pfn)
 			return;
 		pool = page_pool;
 	} else {
@@ -282,7 +259,7 @@ void blk_queue_bounce(struct request_queue *q, struct bio **bio_orig)
 	/*
 	 * slow path
 	 */
-	__blk_queue_bounce(q, bio_orig, pool, must_bounce);
+	__blk_queue_bounce(q, bio_orig, pool);
 }
 
 EXPORT_SYMBOL(blk_queue_bounce);

include/linux/blk_types.h

@@ -118,9 +118,8 @@ struct bio {
 #define BIO_USER_MAPPED 4	/* contains user pages */
 #define BIO_NULL_MAPPED 5	/* contains invalid user pages */
 #define BIO_QUIET	6	/* Make BIO Quiet */
-#define BIO_SNAP_STABLE	7	/* bio data must be snapshotted during write */
-#define BIO_CHAIN	8	/* chained bio, ->bi_remaining in effect */
-#define BIO_REFFED	9	/* bio has elevated ->bi_cnt */
+#define BIO_CHAIN	7	/* chained bio, ->bi_remaining in effect */
+#define BIO_REFFED	8	/* bio has elevated ->bi_cnt */
 
 /*
  * Flags starting here get preserved by bio_reset() - this includes