btrfs: allow btrfs_submit_bio to split bios

Currently the I/O submitters have to split bios according to the chunk
stripe boundaries.  This leads to extra lookups in the extent trees and
a lot of boilerplate code.

To drop this requirement, split the bio when __btrfs_map_block returns a
mapping that is smaller than the requested size and keep a count of
pending bios in the original btrfs_bio so that the upper level
completion is only invoked when all clones have completed.

Based on a patch from Qu Wenruo.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/bio.c

@@ -17,6 +17,7 @@
 #include "file-item.h"
 
 static struct bio_set btrfs_bioset;
+static struct bio_set btrfs_clone_bioset;
 static struct bio_set btrfs_repair_bioset;
 static mempool_t btrfs_failed_bio_pool;
 
@@ -38,6 +39,7 @@ static inline void btrfs_bio_init(struct btrfs_bio *bbio,
 	bbio->inode = inode;
 	bbio->end_io = end_io;
 	bbio->private = private;
+	atomic_set(&bbio->pending_ios, 1);
 }
 
 /*
@@ -75,6 +77,59 @@ struct bio *btrfs_bio_clone_partial(struct bio *orig, u64 offset, u64 size,
 	return bio;
 }
 
+static struct bio *btrfs_split_bio(struct bio *orig, u64 map_length)
+{
+	struct btrfs_bio *orig_bbio = btrfs_bio(orig);
+	struct bio *bio;
+
+	bio = bio_split(orig, map_length >> SECTOR_SHIFT, GFP_NOFS,
+			&btrfs_clone_bioset);
+	btrfs_bio_init(btrfs_bio(bio), orig_bbio->inode, NULL, orig_bbio);
+
+	btrfs_bio(bio)->file_offset = orig_bbio->file_offset;
+	if (!(orig->bi_opf & REQ_BTRFS_ONE_ORDERED))
+		orig_bbio->file_offset += map_length;
+
+	atomic_inc(&orig_bbio->pending_ios);
+	return bio;
+}
+
+static void btrfs_orig_write_end_io(struct bio *bio);
+
+static void btrfs_bbio_propagate_error(struct btrfs_bio *bbio,
+				       struct btrfs_bio *orig_bbio)
+{
+	/*
+	 * For writes we tolerate nr_mirrors - 1 write failures, so we can't
+	 * just blindly propagate a write failure here.  Instead increment the
+	 * error count in the original I/O context so that it is guaranteed to
+	 * be larger than the error tolerance.
+	 */
+	if (bbio->bio.bi_end_io == &btrfs_orig_write_end_io) {
+		struct btrfs_io_stripe *orig_stripe = orig_bbio->bio.bi_private;
+		struct btrfs_io_context *orig_bioc = orig_stripe->bioc;
+
+		atomic_add(orig_bioc->max_errors, &orig_bioc->error);
+	} else {
+		orig_bbio->bio.bi_status = bbio->bio.bi_status;
+	}
+}
+
+static void btrfs_orig_bbio_end_io(struct btrfs_bio *bbio)
+{
+	if (bbio->bio.bi_pool == &btrfs_clone_bioset) {
+		struct btrfs_bio *orig_bbio = bbio->private;
+
+		if (bbio->bio.bi_status)
+			btrfs_bbio_propagate_error(bbio, orig_bbio);
+		bio_put(&bbio->bio);
+		bbio = orig_bbio;
+	}
+
+	if (atomic_dec_and_test(&bbio->pending_ios))
+		bbio->end_io(bbio);
+}
+
 static int next_repair_mirror(struct btrfs_failed_bio *fbio, int cur_mirror)
 {
 	if (cur_mirror == fbio->num_copies)
@@ -92,7 +147,7 @@ static int prev_repair_mirror(struct btrfs_failed_bio *fbio, int cur_mirror)
 static void btrfs_repair_done(struct btrfs_failed_bio *fbio)
 {
 	if (atomic_dec_and_test(&fbio->repair_count)) {
-		fbio->bbio->end_io(fbio->bbio);
+		btrfs_orig_bbio_end_io(fbio->bbio);
 		mempool_free(fbio, &btrfs_failed_bio_pool);
 	}
 }
@@ -229,7 +284,7 @@ static void btrfs_check_read_bio(struct btrfs_bio *bbio, struct btrfs_device *de
 	if (fbio)
 		btrfs_repair_done(fbio);
 	else
-		bbio->end_io(bbio);
+		btrfs_orig_bbio_end_io(bbio);
 }
 
 static void btrfs_log_dev_io_error(struct bio *bio, struct btrfs_device *dev)
@@ -283,7 +338,7 @@ static void btrfs_simple_end_io(struct bio *bio)
 	} else {
 		if (bio_op(bio) == REQ_OP_ZONE_APPEND)
 			btrfs_record_physical_zoned(bbio);
-		bbio->end_io(bbio);
+		btrfs_orig_bbio_end_io(bbio);
 	}
 }
 
@@ -297,7 +352,7 @@ static void btrfs_raid56_end_io(struct bio *bio)
 	if (bio_op(bio) == REQ_OP_READ && !(bbio->bio.bi_opf & REQ_META))
 		btrfs_check_read_bio(bbio, NULL);
 	else
-		bbio->end_io(bbio);
+		btrfs_orig_bbio_end_io(bbio);
 
 	btrfs_put_bioc(bioc);
 }
@@ -324,7 +379,7 @@ static void btrfs_orig_write_end_io(struct bio *bio)
 	else
 		bio->bi_status = BLK_STS_OK;
 
-	bbio->end_io(bbio);
+	btrfs_orig_bbio_end_io(bbio);
 	btrfs_put_bioc(bioc);
 }
 
@@ -488,7 +543,7 @@ static void run_one_async_done(struct btrfs_work *work)
 
 	/* If an error occurred we just want to clean up the bio and move on. */
 	if (bio->bi_status) {
-		btrfs_bio_end_io(async->bbio, bio->bi_status);
+		btrfs_orig_bbio_end_io(async->bbio);
 		return;
 	}
 
@@ -563,9 +618,11 @@ static bool btrfs_wq_submit_bio(struct btrfs_bio *bbio,
 	return true;
 }
 
-void btrfs_submit_bio(struct btrfs_fs_info *fs_info, struct bio *bio, int mirror_num)
+static bool btrfs_submit_chunk(struct btrfs_fs_info *fs_info, struct bio *bio,
+			       int mirror_num)
 {
 	struct btrfs_bio *bbio = btrfs_bio(bio);
+	struct btrfs_bio *orig_bbio = bbio;
 	u64 logical = bio->bi_iter.bi_sector << 9;
 	u64 length = bio->bi_iter.bi_size;
 	u64 map_length = length;
@@ -582,11 +639,10 @@ void btrfs_submit_bio(struct btrfs_fs_info *fs_info, struct bio *bio, int mirror
 		goto fail;
 	}
 
+	map_length = min(map_length, length);
 	if (map_length < length) {
-		btrfs_crit(fs_info,
+		bio = btrfs_split_bio(bio, map_length);
-			   "mapping failed logical %llu bio len %llu len %llu",
+		bbio = btrfs_bio(bio);
-			   logical, length, map_length);
-		BUG();
 	}
 
 	/*
@@ -597,14 +653,14 @@ void btrfs_submit_bio(struct btrfs_fs_info *fs_info, struct bio *bio, int mirror
 		bbio->saved_iter = bio->bi_iter;
 		ret = btrfs_lookup_bio_sums(bbio);
 		if (ret)
-			goto fail;
+			goto fail_put_bio;
 	}
 
 	if (btrfs_op(bio) == BTRFS_MAP_WRITE) {
 		if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
 			ret = btrfs_extract_ordered_extent(btrfs_bio(bio));
 			if (ret)
-				goto fail;
+				goto fail_put_bio;
 		}
 
 		/*
@@ -616,20 +672,32 @@ void btrfs_submit_bio(struct btrfs_fs_info *fs_info, struct bio *bio, int mirror
 		    !btrfs_is_data_reloc_root(bbio->inode->root)) {
 			if (should_async_write(bbio) &&
 			    btrfs_wq_submit_bio(bbio, bioc, &smap, mirror_num))
-				return;
+				goto done;
 
 			ret = btrfs_bio_csum(bbio);
 			if (ret)
-				goto fail;
+				goto fail_put_bio;
 		}
 	}
 
 	__btrfs_submit_bio(bio, bioc, &smap, mirror_num);
-	return;
+done:
+	return map_length == length;
 
+fail_put_bio:
+	if (map_length < length)
+		bio_put(bio);
 fail:
 	btrfs_bio_counter_dec(fs_info);
-	btrfs_bio_end_io(bbio, ret);
+	btrfs_bio_end_io(orig_bbio, ret);
+	/* Do not submit another chunk */
+	return true;
+}
+
+void btrfs_submit_bio(struct btrfs_fs_info *fs_info, struct bio *bio, int mirror_num)
+{
+	while (!btrfs_submit_chunk(fs_info, bio, mirror_num))
+		;
 }
 
 /*
@@ -737,10 +805,13 @@ int __init btrfs_bioset_init(void)
 			offsetof(struct btrfs_bio, bio),
 			BIOSET_NEED_BVECS))
 		return -ENOMEM;
+	if (bioset_init(&btrfs_clone_bioset, BIO_POOL_SIZE,
+			offsetof(struct btrfs_bio, bio), 0))
+		goto out_free_bioset;
 	if (bioset_init(&btrfs_repair_bioset, BIO_POOL_SIZE,
 			offsetof(struct btrfs_bio, bio),
 			BIOSET_NEED_BVECS))
-		goto out_free_bioset;
+		goto out_free_clone_bioset;
 	if (mempool_init_kmalloc_pool(&btrfs_failed_bio_pool, BIO_POOL_SIZE,
 				      sizeof(struct btrfs_failed_bio)))
 		goto out_free_repair_bioset;
@@ -748,6 +819,8 @@ int __init btrfs_bioset_init(void)
 
 out_free_repair_bioset:
 	bioset_exit(&btrfs_repair_bioset);
+out_free_clone_bioset:
+	bioset_exit(&btrfs_clone_bioset);
 out_free_bioset:
 	bioset_exit(&btrfs_bioset);
 	return -ENOMEM;
@@ -757,5 +830,6 @@ void __cold btrfs_bioset_exit(void)
 {
 	mempool_exit(&btrfs_failed_bio_pool);
 	bioset_exit(&btrfs_repair_bioset);
+	bioset_exit(&btrfs_clone_bioset);
 	bioset_exit(&btrfs_bioset);
 }

fs/btrfs/bio.h

@@ -55,6 +55,7 @@ struct btrfs_bio {
 
 	/* For internal use in read end I/O handling */
 	unsigned int mirror_num;
+	atomic_t pending_ios;
 	struct work_struct end_io_work;
 
 	/*