btrfs: don't use btrfs_bio_wq_end_io for compressed writes

Compressed write bio completion is the only user of btrfs_bio_wq_end_io
for writes, and the use of btrfs_bio_wq_end_io is a little suboptimal
here as we only real need user context for the final completion of a
compressed_bio structure, and not every single bio completion.

Add a work_struct to struct compressed_bio instead and use that to call
finish_compressed_bio_write.  This allows to remove all handling of
write bios in the btrfs_bio_wq_end_io infrastructure.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/compression.c

@@ -398,6 +398,14 @@ static void finish_compressed_bio_write(struct compressed_bio *cb)
 	kfree(cb);
 }
 
+static void btrfs_finish_compressed_write_work(struct work_struct *work)
+{
+	struct compressed_bio *cb =
+		container_of(work, struct compressed_bio, write_end_work);
+
+	finish_compressed_bio_write(cb);
+}
+
 /*
  * Do the cleanup once all the compressed pages hit the disk.  This will clear
  * writeback on the file pages and free the compressed pages.
@@ -409,29 +417,15 @@ static void end_compressed_bio_write(struct bio *bio)
 {
 	struct compressed_bio *cb = bio->bi_private;
 
-	if (!dec_and_test_compressed_bio(cb, bio))
-		goto out;
-
-	btrfs_record_physical_zoned(cb->inode, cb->start, bio);
+	if (dec_and_test_compressed_bio(cb, bio)) {
+		struct btrfs_fs_info *fs_info = btrfs_sb(cb->inode->i_sb);
 
-	finish_compressed_bio_write(cb);
-out:
+		btrfs_record_physical_zoned(cb->inode, cb->start, bio);
+		queue_work(fs_info->compressed_write_workers, &cb->write_end_work);
+	}
 	bio_put(bio);
 }
 
-static blk_status_t submit_compressed_bio(struct btrfs_fs_info *fs_info,
-					  struct bio *bio, int mirror_num)
-{
-	blk_status_t ret;
-
-	ASSERT(bio->bi_iter.bi_size);
-	ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA);
-	if (ret)
-		return ret;
-	ret = btrfs_map_bio(fs_info, bio, mirror_num);
-	return ret;
-}
-
 /*
  * Allocate a compressed_bio, which will be used to read/write on-disk
  * (aka, compressed) * data.
@@ -528,7 +522,7 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 	cb->compressed_pages = compressed_pages;
 	cb->compressed_len = compressed_len;
 	cb->writeback = writeback;
-	cb->orig_bio = NULL;
+	INIT_WORK(&cb->write_end_work, btrfs_finish_compressed_write_work);
 	cb->nr_pages = nr_pages;
 
 	if (blkcg_css)
@@ -598,7 +592,8 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 					goto finish_cb;
 			}
 
-			ret = submit_compressed_bio(fs_info, bio, 0);
+			ASSERT(bio->bi_iter.bi_size);
+			ret = btrfs_map_bio(fs_info, bio, 0);
 			if (ret)
 				goto finish_cb;
 			bio = NULL;
@@ -935,7 +930,12 @@ void btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 						  fs_info->sectorsize);
 			sums += fs_info->csum_size * nr_sectors;
 
-			ret = submit_compressed_bio(fs_info, comp_bio, mirror_num);
+			ASSERT(comp_bio->bi_iter.bi_size);
+			ret = btrfs_bio_wq_end_io(fs_info, comp_bio,
+						  BTRFS_WQ_ENDIO_DATA);
+			if (ret)
+				goto finish_cb;
+			ret = btrfs_map_bio(fs_info, comp_bio, mirror_num);
 			if (ret)
 				goto finish_cb;
 			comp_bio = NULL;

fs/btrfs/compression.h

@@ -61,8 +61,11 @@ struct compressed_bio {
 	blk_status_t status;
 	int mirror_num;
 
-	/* for reads, this is the bio we are copying the data into */
-	struct bio *orig_bio;
+	union {
+		/* For reads, this is the bio we are copying the data into */
+		struct bio *orig_bio;
+		struct work_struct write_end_work;
+	};
 
 	/*
 	 * the start of a variable length array of checksums only

fs/btrfs/ctree.h

@@ -854,7 +854,7 @@ struct btrfs_fs_info {
 	struct btrfs_workqueue *endio_meta_workers;
 	struct workqueue_struct *endio_raid56_workers;
 	struct workqueue_struct *rmw_workers;
-	struct btrfs_workqueue *endio_meta_write_workers;
+	struct workqueue_struct *compressed_write_workers;
 	struct btrfs_workqueue *endio_write_workers;
 	struct btrfs_workqueue *endio_freespace_worker;
 	struct btrfs_workqueue *caching_workers;

fs/btrfs/disk-io.c

@@ -749,19 +749,10 @@ static void end_workqueue_bio(struct bio *bio)
 	fs_info = end_io_wq->info;
 	end_io_wq->status = bio->bi_status;
 
-	if (btrfs_op(bio) == BTRFS_MAP_WRITE) {
-		if (end_io_wq->metadata == BTRFS_WQ_ENDIO_METADATA)
-			wq = fs_info->endio_meta_write_workers;
-		else if (end_io_wq->metadata == BTRFS_WQ_ENDIO_FREE_SPACE)
-			wq = fs_info->endio_freespace_worker;
-		else
-			wq = fs_info->endio_write_workers;
-	} else {
-		if (end_io_wq->metadata)
-			wq = fs_info->endio_meta_workers;
-		else
-			wq = fs_info->endio_workers;
-	}
+	if (end_io_wq->metadata)
+		wq = fs_info->endio_meta_workers;
+	else
+		wq = fs_info->endio_workers;
 
 	btrfs_init_work(&end_io_wq->work, end_workqueue_fn, NULL, NULL);
 	btrfs_queue_work(wq, &end_io_wq->work);
@@ -772,6 +763,9 @@ blk_status_t btrfs_bio_wq_end_io(struct btrfs_fs_info *info, struct bio *bio,
 {
 	struct btrfs_end_io_wq *end_io_wq;
 
+	if (WARN_ON_ONCE(btrfs_op(bio) != BTRFS_MAP_WRITE))
+		return BLK_STS_IOERR;
+
 	end_io_wq = kmem_cache_alloc(btrfs_end_io_wq_cache, GFP_NOFS);
 	if (!end_io_wq)
 		return BLK_STS_RESOURCE;
@@ -2281,6 +2275,8 @@ static void btrfs_stop_all_workers(struct btrfs_fs_info *fs_info)
 		destroy_workqueue(fs_info->endio_raid56_workers);
 	if (fs_info->rmw_workers)
 		destroy_workqueue(fs_info->rmw_workers);
+	if (fs_info->compressed_write_workers)
+		destroy_workqueue(fs_info->compressed_write_workers);
 	btrfs_destroy_workqueue(fs_info->endio_write_workers);
 	btrfs_destroy_workqueue(fs_info->endio_freespace_worker);
 	btrfs_destroy_workqueue(fs_info->delayed_workers);
@@ -2295,7 +2291,6 @@ static void btrfs_stop_all_workers(struct btrfs_fs_info *fs_info)
 	 * queues can do metadata I/O operations.
 	 */
 	btrfs_destroy_workqueue(fs_info->endio_meta_workers);
-	btrfs_destroy_workqueue(fs_info->endio_meta_write_workers);
 }
 
 static void free_root_extent_buffers(struct btrfs_root *root)
@@ -2483,15 +2478,14 @@ static int btrfs_init_workqueues(struct btrfs_fs_info *fs_info)
 	fs_info->endio_meta_workers =
 		btrfs_alloc_workqueue(fs_info, "endio-meta", flags,
 				      max_active, 4);
-	fs_info->endio_meta_write_workers =
-		btrfs_alloc_workqueue(fs_info, "endio-meta-write", flags,
-				      max_active, 2);
 	fs_info->endio_raid56_workers =
 		alloc_workqueue("btrfs-endio-raid56", flags, max_active);
 	fs_info->rmw_workers = alloc_workqueue("btrfs-rmw", flags, max_active);
 	fs_info->endio_write_workers =
 		btrfs_alloc_workqueue(fs_info, "endio-write", flags,
 				      max_active, 2);
+	fs_info->compressed_write_workers =
+		alloc_workqueue("btrfs-compressed-write", flags, max_active);
 	fs_info->endio_freespace_worker =
 		btrfs_alloc_workqueue(fs_info, "freespace-write", flags,
 				      max_active, 0);
@@ -2506,7 +2500,7 @@ static int btrfs_init_workqueues(struct btrfs_fs_info *fs_info)
 	if (!(fs_info->workers && fs_info->hipri_workers &&
 	      fs_info->delalloc_workers && fs_info->flush_workers &&
 	      fs_info->endio_workers && fs_info->endio_meta_workers &&
-	      fs_info->endio_meta_write_workers &&
+	      fs_info->compressed_write_workers &&
 	      fs_info->endio_write_workers && fs_info->endio_raid56_workers &&
 	      fs_info->endio_freespace_worker && fs_info->rmw_workers &&
 	      fs_info->caching_workers && fs_info->fixup_workers &&

fs/btrfs/super.c

@@ -1934,8 +1934,6 @@ static void btrfs_resize_thread_pool(struct btrfs_fs_info *fs_info,
 	btrfs_workqueue_set_max(fs_info->caching_workers, new_pool_size);
 	btrfs_workqueue_set_max(fs_info->endio_workers, new_pool_size);
 	btrfs_workqueue_set_max(fs_info->endio_meta_workers, new_pool_size);
-	btrfs_workqueue_set_max(fs_info->endio_meta_write_workers,
-				new_pool_size);
 	btrfs_workqueue_set_max(fs_info->endio_write_workers, new_pool_size);
 	btrfs_workqueue_set_max(fs_info->endio_freespace_worker, new_pool_size);
 	btrfs_workqueue_set_max(fs_info->delayed_workers, new_pool_size);