btrfs: handle checksum generation in the storage layer

Instead of letting the callers of btrfs_submit_bio deal with checksumming
the (meta)data in the bio and making decisions on when to offload the
checksumming to the bio, leave that to btrfs_submit_bio.  Do do so the
existing btrfs_submit_bio function is split into an upper and a lower
half, so that the lower half can be offloaded to a workqueue.

Note that this changes the behavior for direct writes to raid56 volumes so
that async checksum offloading is not skipped when more I/O is expected.
This runs counter to the argument explaining why it was done, although I
can't measure any affects of the change.  Commits later in this series
will make sure the entire direct writes is offloaded to the workqueue
at once and thus make sure it is sent to the raid56 code from a single
thread.

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

fs/btrfs/bio.c

@@ -401,6 +401,166 @@ static void btrfs_submit_mirrored_bio(struct btrfs_io_context *bioc, int dev_nr)
 	btrfs_submit_dev_bio(bioc->stripes[dev_nr].dev, bio);
 }
 
+static void __btrfs_submit_bio(struct bio *bio, struct btrfs_io_context *bioc,
+			       struct btrfs_io_stripe *smap, int mirror_num)
+{
+	/* Do not leak our private flag into the block layer. */
+	bio->bi_opf &= ~REQ_BTRFS_ONE_ORDERED;
+
+	if (!bioc) {
+		/* Single mirror read/write fast path. */
+		btrfs_bio(bio)->mirror_num = mirror_num;
+		bio->bi_iter.bi_sector = smap->physical >> SECTOR_SHIFT;
+		bio->bi_private = smap->dev;
+		bio->bi_end_io = btrfs_simple_end_io;
+		btrfs_submit_dev_bio(smap->dev, bio);
+	} else if (bioc->map_type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
+		/* Parity RAID write or read recovery. */
+		bio->bi_private = bioc;
+		bio->bi_end_io = btrfs_raid56_end_io;
+		if (bio_op(bio) == REQ_OP_READ)
+			raid56_parity_recover(bio, bioc, mirror_num);
+		else
+			raid56_parity_write(bio, bioc);
+	} else {
+		/* Write to multiple mirrors. */
+		int total_devs = bioc->num_stripes;
+
+		bioc->orig_bio = bio;
+		for (int dev_nr = 0; dev_nr < total_devs; dev_nr++)
+			btrfs_submit_mirrored_bio(bioc, dev_nr);
+	}
+}
+
+static blk_status_t btrfs_bio_csum(struct btrfs_bio *bbio)
+{
+	if (bbio->bio.bi_opf & REQ_META)
+		return btree_csum_one_bio(&bbio->bio);
+	return btrfs_csum_one_bio(bbio);
+}
+
+/*
+ * Async submit bios are used to offload expensive checksumming onto the worker
+ * threads.
+ */
+struct async_submit_bio {
+	struct btrfs_bio *bbio;
+	struct btrfs_io_context *bioc;
+	struct btrfs_io_stripe smap;
+	int mirror_num;
+	struct btrfs_work work;
+};
+
+/*
+ * In order to insert checksums into the metadata in large chunks, we wait
+ * until bio submission time.   All the pages in the bio are checksummed and
+ * sums are attached onto the ordered extent record.
+ *
+ * At IO completion time the csums attached on the ordered extent record are
+ * inserted into the btree.
+ */
+static void run_one_async_start(struct btrfs_work *work)
+{
+	struct async_submit_bio *async =
+		container_of(work, struct async_submit_bio, work);
+	blk_status_t ret;
+
+	ret = btrfs_bio_csum(async->bbio);
+	if (ret)
+		async->bbio->bio.bi_status = ret;
+}
+
+/*
+ * In order to insert checksums into the metadata in large chunks, we wait
+ * until bio submission time.   All the pages in the bio are checksummed and
+ * sums are attached onto the ordered extent record.
+ *
+ * At IO completion time the csums attached on the ordered extent record are
+ * inserted into the tree.
+ */
+static void run_one_async_done(struct btrfs_work *work)
+{
+	struct async_submit_bio *async =
+		container_of(work, struct async_submit_bio, work);
+	struct bio *bio = &async->bbio->bio;
+
+	/* 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);
+		return;
+	}
+
+	/*
+	 * All of the bios that pass through here are from async helpers.
+	 * Use REQ_CGROUP_PUNT to issue them from the owning cgroup's context.
+	 * This changes nothing when cgroups aren't in use.
+	 */
+	bio->bi_opf |= REQ_CGROUP_PUNT;
+	__btrfs_submit_bio(bio, async->bioc, &async->smap, async->mirror_num);
+}
+
+static void run_one_async_free(struct btrfs_work *work)
+{
+	kfree(container_of(work, struct async_submit_bio, work));
+}
+
+static bool should_async_write(struct btrfs_bio *bbio)
+{
+	/*
+	 * If the I/O is not issued by fsync and friends, (->sync_writers != 0),
+	 * then try to defer the submission to a workqueue to parallelize the
+	 * checksum calculation.
+	 */
+	if (atomic_read(&bbio->inode->sync_writers))
+		return false;
+
+	/*
+	 * Submit metadata writes synchronously if the checksum implementation
+	 * is fast, or we are on a zoned device that wants I/O to be submitted
+	 * in order.
+	 */
+	if (bbio->bio.bi_opf & REQ_META) {
+		struct btrfs_fs_info *fs_info = bbio->inode->root->fs_info;
+
+		if (btrfs_is_zoned(fs_info))
+			return false;
+		if (test_bit(BTRFS_FS_CSUM_IMPL_FAST, &fs_info->flags))
+			return false;
+	}
+
+	return true;
+}
+
+/*
+ * Submit bio to an async queue.
+ *
+ * Return true if the work has been succesfuly submitted, else false.
+ */
+static bool btrfs_wq_submit_bio(struct btrfs_bio *bbio,
+				struct btrfs_io_context *bioc,
+				struct btrfs_io_stripe *smap, int mirror_num)
+{
+	struct btrfs_fs_info *fs_info = bbio->inode->root->fs_info;
+	struct async_submit_bio *async;
+
+	async = kmalloc(sizeof(*async), GFP_NOFS);
+	if (!async)
+		return false;
+
+	async->bbio = bbio;
+	async->bioc = bioc;
+	async->smap = *smap;
+	async->mirror_num = mirror_num;
+
+	btrfs_init_work(&async->work, run_one_async_start, run_one_async_done,
+			run_one_async_free);
+	if (op_is_sync(bbio->bio.bi_opf))
+		btrfs_queue_work(fs_info->hipri_workers, &async->work);
+	else
+		btrfs_queue_work(fs_info->workers, &async->work);
+	return true;
+}
+
 void btrfs_submit_bio(struct btrfs_fs_info *fs_info, struct bio *bio, int mirror_num)
 {
 	struct btrfs_bio *bbio = btrfs_bio(bio);
@@ -438,33 +598,25 @@ void btrfs_submit_bio(struct btrfs_fs_info *fs_info, struct bio *bio, int mirror
 			goto fail;
 	}
 
-	/* Do not leak our private flag into the block layer. */
-	bio->bi_opf &= ~REQ_BTRFS_ONE_ORDERED;
-
-	if (!bioc) {
-		/* Single mirror read/write fast path */
-		bbio->mirror_num = mirror_num;
-		bio->bi_iter.bi_sector = smap.physical >> SECTOR_SHIFT;
-		bio->bi_private = smap.dev;
-		bio->bi_end_io = btrfs_simple_end_io;
-		btrfs_submit_dev_bio(smap.dev, bio);
-	} else if (bioc->map_type & BTRFS_BLOCK_GROUP_RAID56_MASK) {
-		/* Parity RAID write or read recovery */
-		bio->bi_private = bioc;
-		bio->bi_end_io = btrfs_raid56_end_io;
-		if (bio_op(bio) == REQ_OP_READ)
-			raid56_parity_recover(bio, bioc, mirror_num);
-		else
-			raid56_parity_write(bio, bioc);
-	} else {
-		/* Write to multiple mirrors */
-		int total_devs = bioc->num_stripes;
-		int dev_nr;
-
-		bioc->orig_bio = bio;
-		for (dev_nr = 0; dev_nr < total_devs; dev_nr++)
-			btrfs_submit_mirrored_bio(bioc, dev_nr);
+	if (btrfs_op(bio) == BTRFS_MAP_WRITE) {
+		/*
+		 * Csum items for reloc roots have already been cloned at this
+		 * point, so they are handled as part of the no-checksum case.
+		 */
+		if (!(bbio->inode->flags & BTRFS_INODE_NODATASUM) &&
+		    !test_bit(BTRFS_FS_STATE_NO_CSUMS, &fs_info->fs_state) &&
+		    !btrfs_is_data_reloc_root(bbio->inode->root)) {
+			if (should_async_write(bbio) &&
+			    btrfs_wq_submit_bio(bbio, bioc, &smap, mirror_num))
+				return;
+
+			ret = btrfs_bio_csum(bbio);
+			if (ret)
+				goto fail;
+		}
 	}
+
+	__btrfs_submit_bio(bio, bioc, &smap, mirror_num);
 	return;
 
 fail:

fs/btrfs/compression.c

@@ -355,7 +355,6 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 	u64 cur_disk_bytenr = disk_start;
 	u64 next_stripe_start;
 	blk_status_t ret = BLK_STS_OK;
-	int skip_sum = inode->flags & BTRFS_INODE_NODATASUM;
 	const bool use_append = btrfs_use_zone_append(inode, disk_start);
 	const enum req_op bio_op = REQ_BTRFS_ONE_ORDERED |
 				   (use_append ? REQ_OP_ZONE_APPEND : REQ_OP_WRITE);
@@ -437,14 +436,6 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 			submit = true;
 
 		if (submit) {
-			if (!skip_sum) {
-				ret = btrfs_csum_one_bio(btrfs_bio(bio));
-				if (ret) {
-					btrfs_bio_end_io(btrfs_bio(bio), ret);
-					break;
-				}
-			}
-
 			ASSERT(bio->bi_iter.bi_size);
 			btrfs_submit_bio(fs_info, bio, 0);
 			bio = NULL;