[PATCH v4 0/9] btrfs: compression: refactor and enhancement preparing for subpage compression support

[PATCH v4 0/9] btrfs: compression: refactor and enhancement preparing for subpage compression support

[Qu Wenruo]

There are quite some problems in compression code:

- Weird compressed_bio::pending_bios dance
  If we just don't want compressed_bio being freed halfway, we have more
  sane methods, just like btrfs_subpage::readers.

  So here we fix it by introducing compressed_bio::io_sectors to do the
  job.

- BUG_ON()s inside btrfs_submit_compressed_*()
  Even they are just ENOMEM, we should handle them.
  With io_sectors introduced, we have a way to finish compressed_bio
  all by ourselves, as long as we haven't submitted last bio.

  If we have last bio submitted, then endio will handle it well.

- Duplicated code for compressed bio allocation and submission
  Just small refactor can handle it

- Stripe boundary is checked every time one page is added
  This is overkilled.
  Just learn from extent_io.c refactor which use bio_ctrl to do the
  boundary check only once for each bio.

  Although in compression context, we don't need extra checks in
  extent_io.c, thus we don't need bio_ctrl structure, but
  can afford to do it locally.

- Dead code removal
  One dead comment and a new zombie function,
  btrfs_bio_fits_in_stripe(), can be removed now.

Changelog:
v2:
- Rebased to latest misc-next

- Fix a bug in btrfs_submit_compressed_write() where zoned write is not
  taken into consideration

- Reuse the existing chunk mapping of btrfs_get_chunk_map()

v3:
- Fix a bug that zoned device can't even pass btrfs/001
  This is because at endio time, bi_size for zoned device is always 0.
  We have to use bio_for_each_segment_all() to calculate the real bio
  size instead.
  In theory, it should also happen more frequently for non-zoned device,
  but no catch for all test cases (with "-o compress") except btrfs/011.

- Fix btrfs/011 hang when tested with "-o compress"
  This is caused by checking both atomic value without protection.
  Checking two atomic values is no longer atomic.

  In fact, with compressed_bio::io_sectors introduced, pending_bios is
  only used to wait for any pending bio to finish in error path.

  Thus dec_and_test_compressed_bio() only need to check if io_sectors is
  zero

- Fix a error that in error handling path, we may hang due to missing
  wake_up() in dec_and_test_compressed_bio()

v4:
- Use formal words for BUG_ON() removal patch titles

- Remove compressed_bio::pending_bios
  As compressed_bio::pending_sectors can replace it completely

- Remove unnecessary comments and BUG_ON()s

- Use wait_var_event() APIs to reduce the memory overhead

- Comments update to follow the same schema for moved comments

Qu Wenruo (9):
  btrfs: remove a dead comment for btrfs_decompress_bio()
  btrfs: introduce compressed_bio::pending_sectors to trace compressed
    bio more elegantly
  btrfs: handle errors properly inside btrfs_submit_compressed_read()
  btrfs: handle errors properly inside btrfs_submit_compressed_write()
  btrfs: introduce submit_compressed_bio() for compression
  btrfs: introduce alloc_compressed_bio() for compression
  btrfs: make btrfs_submit_compressed_read() to determine stripe
    boundary at bio allocation time
  btrfs: make btrfs_submit_compressed_write() to determine stripe
    boundary at bio allocation time
  btrfs: remove unused function btrfs_bio_fits_in_stripe()

 fs/btrfs/compression.c | 587 +++++++++++++++++++++++------------------
 fs/btrfs/compression.h |   4 +-
 fs/btrfs/ctree.h       |   2 -
 fs/btrfs/inode.c       |  42 ---
 4 files changed, 336 insertions(+), 299 deletions(-)

-- 
2.32.0

[PATCH v4 1/9] btrfs: remove a dead comment for btrfs_decompress_bio()

[Qu Wenruo]

Since commit 8140dc30a432 ("btrfs: btrfs_decompress_bio() could accept
compressed_bio instead"), btrfs_decompress_bio() accepts
"struct compressed_bio" other than open-coded parameter list.

Thus the comments for the parameter list is no longer needed.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
---
 fs/btrfs/compression.c | 14 --------------
 1 file changed, 14 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 35ca49893803..9a023ae0f98b 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -1212,20 +1212,6 @@ int btrfs_compress_pages(unsigned int type_level, struct address_space *mapping,
 	return ret;
 }
 
-/*
- * pages_in is an array of pages with compressed data.
- *
- * disk_start is the starting logical offset of this array in the file
- *
- * orig_bio contains the pages from the file that we want to decompress into
- *
- * srclen is the number of bytes in pages_in
- *
- * The basic idea is that we have a bio that was created by readpages.
- * The pages in the bio are for the uncompressed data, and they may not
- * be contiguous.  They all correspond to the range of bytes covered by
- * the compressed extent.
- */
 static int btrfs_decompress_bio(struct compressed_bio *cb)
 {
 	struct list_head *workspace;
-- 
2.32.0

[PATCH v4 2/9] btrfs: introduce compressed_bio::pending_sectors to trace compressed bio more elegantly

[Qu Wenruo]

For btrfs_submit_compressed_read() and btrfs_submit_compressed_write(),
we have a pretty weird dance around compressed_bio::pending_bios:

  btrfs_submit_compressed_read/write()
  {
	cb = kmalloc()
	refcount_set(&cb->pending_bios, 0);
	bio = btrfs_alloc_bio();

	/* NOTE here, we haven't yet submitted any bio */
	refcount_set(&cb->pending_bios, 1);

	for (pg_index = 0; pg_index < cb->nr_pages; pg_index++) {
		if (submit) {
			/* Here we submit bio, but we always have one
			 * extra pending_bios */
			refcount_inc(&cb->pending_bios);
			ret = btrfs_map_bio();
		}
	}

	/* Submit the last bio */
	ret = btrfs_map_bio();
  }

There are two reasons why we do this:

- compressed_bio::pending_bios is a refcount
  Thus if it's reduced to 0, it can not be increased again.

- To ensure the compressed_bio is not freed by some submitted bios
  If the submitted bio is finished before the next bio submitted,
  we can free the compressed_bio completely.

But the above code is sometimes confusing, and we can do it better by
just introduce a new member, compressed_bio::pending_sectors.

Now we use compressed_bio::pending_sectors to indicate whether we have any
pending sectors under IO or not yet submitted.

If pending_sectors == 0, we're definitely the last bio of compressed_bio, and
is OK to release the compressed bio.

Now the workflow looks like this:

  btrfs_submit_compressed_read/write()
  {
	cb = kmalloc()
	atomic_set(&cb->pending_bios, 0);
	refcount_set(&cb->pending_sectors,
		     compressed_len >> sectorsize_bits);
	bio = btrfs_alloc_bio();

	for (pg_index = 0; pg_index < cb->nr_pages; pg_index++) {
		if (submit) {
			refcount_inc(&cb->pending_bios);
			ret = btrfs_map_bio();
		}
	}

	/* Submit the last bio */
	refcount_inc(&cb->pending_bios);
	ret = btrfs_map_bio();
  }

For now we still need pending_bios for later error handling, but will
remove pending_bios eventually after properly handling the errors.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/compression.c | 78 ++++++++++++++++++++++++------------------
 fs/btrfs/compression.h |  5 ++-
 2 files changed, 49 insertions(+), 34 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 9a023ae0f98b..b84b9f7420c2 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -193,6 +193,39 @@ static int check_compressed_csum(struct btrfs_inode *inode, struct bio *bio,
 	return 0;
 }
 
+/*
+ * Reduce bio and io accounting for a compressed_bio with its coresponding bio.
+ *
+ * Return true if there is no pending bio nor io.
+ * Return false otherwise.
+ */
+static bool dec_and_test_compressed_bio(struct compressed_bio *cb,
+					struct bio *bio)
+{
+	struct btrfs_fs_info *fs_info = btrfs_sb(cb->inode->i_sb);
+	unsigned int bi_size = 0;
+	bool last_io = false;
+	struct bio_vec *bvec;
+	struct bvec_iter_all iter_all;
+
+	/*
+	 * At endio time, bi_iter.bi_size doesn't represent the real bio size.
+	 * Thus here we have to iterate through all segments to grab correct
+	 * bio size.
+	 */
+	bio_for_each_segment_all(bvec, bio, iter_all)
+		bi_size += bvec->bv_len;
+
+	if (bio->bi_status)
+		cb->errors = 1;
+
+	ASSERT(bi_size && bi_size <= cb->compressed_len);
+	last_io = refcount_sub_and_test(bi_size >> fs_info->sectorsize_bits,
+					&cb->pending_sectors);
+	atomic_dec(&cb->pending_bios);
+	return last_io;
+}
+
 /* when we finish reading compressed pages from the disk, we
  * decompress them and then run the bio end_io routines on the
  * decompressed pages (in the inode address space).
@@ -212,13 +245,7 @@ static void end_compressed_bio_read(struct bio *bio)
 	unsigned int mirror = btrfs_io_bio(bio)->mirror_num;
 	int ret = 0;
 
-	if (bio->bi_status)
-		cb->errors = 1;
-
-	/* if there are more bios still pending for this compressed
-	 * extent, just exit
-	 */
-	if (!refcount_dec_and_test(&cb->pending_bios))
+	if (!dec_and_test_compressed_bio(cb, bio))
 		goto out;
 
 	/*
@@ -336,13 +363,7 @@ static void end_compressed_bio_write(struct bio *bio)
 	struct page *page;
 	unsigned int index;
 
-	if (bio->bi_status)
-		cb->errors = 1;
-
-	/* if there are more bios still pending for this compressed
-	 * extent, just exit
-	 */
-	if (!refcount_dec_and_test(&cb->pending_bios))
+	if (!dec_and_test_compressed_bio(cb, bio))
 		goto out;
 
 	/* ok, we're the last bio for this extent, step one is to
@@ -408,7 +429,9 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 	cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS);
 	if (!cb)
 		return BLK_STS_RESOURCE;
-	refcount_set(&cb->pending_bios, 0);
+	atomic_set(&cb->pending_bios, 0);
+	refcount_set(&cb->pending_sectors,
+		     compressed_len >> fs_info->sectorsize_bits);
 	cb->errors = 0;
 	cb->inode = &inode->vfs_inode;
 	cb->start = start;
@@ -441,7 +464,6 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 		bio->bi_opf |= REQ_CGROUP_PUNT;
 		kthread_associate_blkcg(blkcg_css);
 	}
-	refcount_set(&cb->pending_bios, 1);
 
 	/* create and submit bios for the compressed pages */
 	bytes_left = compressed_len;
@@ -469,13 +491,7 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 
 		page->mapping = NULL;
 		if (submit || len < PAGE_SIZE) {
-			/*
-			 * inc the count before we submit the bio so
-			 * we know the end IO handler won't happen before
-			 * we inc the count.  Otherwise, the cb might get
-			 * freed before we're done setting it up
-			 */
-			refcount_inc(&cb->pending_bios);
+			atomic_inc(&cb->pending_bios);
 			ret = btrfs_bio_wq_end_io(fs_info, bio,
 						  BTRFS_WQ_ENDIO_DATA);
 			BUG_ON(ret); /* -ENOMEM */
@@ -513,6 +529,7 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 		cond_resched();
 	}
 
+	atomic_inc(&cb->pending_bios);
 	ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA);
 	BUG_ON(ret); /* -ENOMEM */
 
@@ -696,7 +713,9 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	if (!cb)
 		goto out;
 
-	refcount_set(&cb->pending_bios, 0);
+	atomic_set(&cb->pending_bios, 0);
+	refcount_set(&cb->pending_sectors,
+		     compressed_len >> fs_info->sectorsize_bits);
 	cb->errors = 0;
 	cb->inode = inode;
 	cb->mirror_num = mirror_num;
@@ -741,7 +760,6 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	comp_bio->bi_opf = REQ_OP_READ;
 	comp_bio->bi_private = cb;
 	comp_bio->bi_end_io = end_compressed_bio_read;
-	refcount_set(&cb->pending_bios, 1);
 
 	for (pg_index = 0; pg_index < nr_pages; pg_index++) {
 		u32 pg_len = PAGE_SIZE;
@@ -770,18 +788,11 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 		if (submit || bio_add_page(comp_bio, page, pg_len, 0) < pg_len) {
 			unsigned int nr_sectors;
 
+			atomic_inc(&cb->pending_bios);
 			ret = btrfs_bio_wq_end_io(fs_info, comp_bio,
 						  BTRFS_WQ_ENDIO_DATA);
 			BUG_ON(ret); /* -ENOMEM */
 
-			/*
-			 * inc the count before we submit the bio so
-			 * we know the end IO handler won't happen before
-			 * we inc the count.  Otherwise, the cb might get
-			 * freed before we're done setting it up
-			 */
-			refcount_inc(&cb->pending_bios);
-
 			ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
 			BUG_ON(ret); /* -ENOMEM */
 
@@ -805,6 +816,7 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 		cur_disk_byte += pg_len;
 	}
 
+	atomic_inc(&cb->pending_bios);
 	ret = btrfs_bio_wq_end_io(fs_info, comp_bio, BTRFS_WQ_ENDIO_DATA);
 	BUG_ON(ret); /* -ENOMEM */
 
diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
index c359f20920d0..8940e9e9fed3 100644
--- a/fs/btrfs/compression.h
+++ b/fs/btrfs/compression.h
@@ -29,7 +29,10 @@ struct btrfs_inode;
 
 struct compressed_bio {
 	/* number of bios pending for this compressed extent */
-	refcount_t pending_bios;
+	atomic_t pending_bios;
+
+	/* Number of sectors with unfinished IO (unsubmitted or unfinished) */
+	refcount_t pending_sectors;
 
 	/* Number of compressed pages in the array */
 	unsigned int nr_pages;
-- 
2.32.0

[PATCH v4 3/9] btrfs: handle errors properly inside btrfs_submit_compressed_read()

[Qu Wenruo]

There are quite some BUG_ON()s inside btrfs_submit_compressed_read(),
namingly all errors inside the for() loop relies on BUG_ON() to handle
-ENOMEM.

Handle these errors properly by:

- Wait for submitted bios to finish first
  Using wake_var_event() APIs to wait without introducing extra memory
  overhead inside compressed_bio.
  This allows us to wait for any submitted bio to finish, while still
  keeps the compressed_bio from being freed.

- Introduce finish_compressed_bio_read() to finish the compressed_bio

- Properly end the bio and finish compressed_bio when error happens

Now in btrfs_submit_compressed_read() even when the bio submission
failed, we can properly handle the error without triggering BUG_ON().

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/compression.c | 121 ++++++++++++++++++++++++++---------------
 1 file changed, 77 insertions(+), 44 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index b84b9f7420c2..81278b04b111 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -223,9 +223,54 @@ static bool dec_and_test_compressed_bio(struct compressed_bio *cb,
 	last_io = refcount_sub_and_test(bi_size >> fs_info->sectorsize_bits,
 					&cb->pending_sectors);
 	atomic_dec(&cb->pending_bios);
+	/*
+	 * Here we must wake up the possible error handler after all other
+	 * operations on @cb finished, or we can race with
+	 * finish_compressed_bio_*() which may free @cb.
+	 */
+	wake_up_var(cb);
+
 	return last_io;
 }
 
+static void finish_compressed_bio_read(struct compressed_bio *cb,
+				       struct bio *bio)
+{
+	unsigned int index;
+	struct page *page;
+
+	/* Release the compressed pages */
+	for (index = 0; index < cb->nr_pages; index++) {
+		page = cb->compressed_pages[index];
+		page->mapping = NULL;
+		put_page(page);
+	}
+
+	/* Do io completion on the original bio */
+	if (cb->errors) {
+		bio_io_error(cb->orig_bio);
+	} else {
+		struct bio_vec *bvec;
+		struct bvec_iter_all iter_all;
+
+		ASSERT(bio);
+		ASSERT(!bio->bi_status);
+		/*
+		 * We have verified the checksum already, set page
+		 * checked so the end_io handlers know about it
+		 */
+		ASSERT(!bio_flagged(bio, BIO_CLONED));
+		bio_for_each_segment_all(bvec, cb->orig_bio, iter_all)
+			SetPageChecked(bvec->bv_page);
+
+		bio_endio(cb->orig_bio);
+	}
+
+	/* Finally free the cb struct */
+	kfree(cb->compressed_pages);
+	kfree(cb);
+}
+
 /* when we finish reading compressed pages from the disk, we
  * decompress them and then run the bio end_io routines on the
  * decompressed pages (in the inode address space).
@@ -240,8 +285,6 @@ static void end_compressed_bio_read(struct bio *bio)
 {
 	struct compressed_bio *cb = bio->bi_private;
 	struct inode *inode;
-	struct page *page;
-	unsigned int index;
 	unsigned int mirror = btrfs_io_bio(bio)->mirror_num;
 	int ret = 0;
 
@@ -276,36 +319,7 @@ static void end_compressed_bio_read(struct bio *bio)
 csum_failed:
 	if (ret)
 		cb->errors = 1;
-
-	/* release the compressed pages */
-	index = 0;
-	for (index = 0; index < cb->nr_pages; index++) {
-		page = cb->compressed_pages[index];
-		page->mapping = NULL;
-		put_page(page);
-	}
-
-	/* do io completion on the original bio */
-	if (cb->errors) {
-		bio_io_error(cb->orig_bio);
-	} else {
-		struct bio_vec *bvec;
-		struct bvec_iter_all iter_all;
-
-		/*
-		 * we have verified the checksum already, set page
-		 * checked so the end_io handlers know about it
-		 */
-		ASSERT(!bio_flagged(bio, BIO_CLONED));
-		bio_for_each_segment_all(bvec, cb->orig_bio, iter_all)
-			SetPageChecked(bvec->bv_page);
-
-		bio_endio(cb->orig_bio);
-	}
-
-	/* finally free the cb struct */
-	kfree(cb->compressed_pages);
-	kfree(cb);
+	finish_compressed_bio_read(cb, bio);
 out:
 	bio_put(bio);
 }
@@ -791,20 +805,20 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 			atomic_inc(&cb->pending_bios);
 			ret = btrfs_bio_wq_end_io(fs_info, comp_bio,
 						  BTRFS_WQ_ENDIO_DATA);
-			BUG_ON(ret); /* -ENOMEM */
+			if (ret)
+				goto finish_cb;
 
 			ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
-			BUG_ON(ret); /* -ENOMEM */
+			if (ret)
+				goto finish_cb;
 
 			nr_sectors = DIV_ROUND_UP(comp_bio->bi_iter.bi_size,
 						  fs_info->sectorsize);
 			sums += fs_info->csum_size * nr_sectors;
 
 			ret = btrfs_map_bio(fs_info, comp_bio, mirror_num);
-			if (ret) {
-				comp_bio->bi_status = ret;
-				bio_endio(comp_bio);
-			}
+			if (ret)
+				goto finish_cb;
 
 			comp_bio = btrfs_bio_alloc(cur_disk_byte);
 			comp_bio->bi_opf = REQ_OP_READ;
@@ -818,16 +832,16 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 
 	atomic_inc(&cb->pending_bios);
 	ret = btrfs_bio_wq_end_io(fs_info, comp_bio, BTRFS_WQ_ENDIO_DATA);
-	BUG_ON(ret); /* -ENOMEM */
+	if (ret)
+		goto last_bio;
 
 	ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
-	BUG_ON(ret); /* -ENOMEM */
+	if (ret)
+		goto last_bio;
 
 	ret = btrfs_map_bio(fs_info, comp_bio, mirror_num);
-	if (ret) {
-		comp_bio->bi_status = ret;
-		bio_endio(comp_bio);
-	}
+	if (ret)
+		goto last_bio;
 
 	return 0;
 
@@ -843,6 +857,25 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 out:
 	free_extent_map(em);
 	return ret;
+last_bio:
+	comp_bio->bi_status = ret;
+	/* This is the last bio, endio functions will free @cb */
+	bio_endio(comp_bio);
+	return ret;
+finish_cb:
+	if (comp_bio) {
+		comp_bio->bi_status = ret;
+		bio_endio(comp_bio);
+	}
+	wait_var_event(cb, atomic_read(&cb->pending_bios) == 0);
+	/*
+	 * Even with previous bio ended, we should still have io not yet
+	 * submitted, thus need to finish @cb manually.
+	 */
+	ASSERT(refcount_read(&cb->pending_sectors));
+	/* Now we are the only one referring @cb, can finish it safely. */
+	finish_compressed_bio_read(cb, NULL);
+	return ret;
 }
 
 /*
-- 
2.32.0

[PATCH v4 4/9] btrfs: handle errors properly inside btrfs_submit_compressed_write()

[Qu Wenruo]

Just like btrfs_submit_compressed_read(), there are quite some BUG_ON()s
inside btrfs_submit_compressed_write() for the bio submission path.

Fix them using the same method:

- For last bio, just endio the bio
  As in that case, one of the endio function of all these submitted bio
  will be able to free the compressed_bio

- For half-submitted bio, wait and finish the compressed_bio manually
  In this case, as long as all other bio finishes, we're the only one
  referring the compressed bio, and can manually finish it.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/compression.c | 101 ++++++++++++++++++++++++++---------------
 1 file changed, 64 insertions(+), 37 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 81278b04b111..a88aee331022 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -362,50 +362,56 @@ static noinline void end_compressed_writeback(struct inode *inode,
 	/* the inode may be gone now */
 }
 
-/*
- * do the cleanup once all the compressed pages hit the disk.
- * This will clear writeback on the file pages and free the compressed
- * pages.
- *
- * This also calls the writeback end hooks for the file pages so that
- * metadata and checksums can be updated in the file.
- */
-static void end_compressed_bio_write(struct bio *bio)
+static void finish_compressed_bio_write(struct compressed_bio *cb)
 {
-	struct compressed_bio *cb = bio->bi_private;
-	struct inode *inode;
-	struct page *page;
+	struct inode *inode = cb->inode;
 	unsigned int index;
 
-	if (!dec_and_test_compressed_bio(cb, bio))
-		goto out;
-
-	/* ok, we're the last bio for this extent, step one is to
-	 * call back into the FS and do all the end_io operations
+	/*
+	 * Ok, we're the last bio for this extent, step one is to
+	 * call back into the FS and do all the end_io operations.
 	 */
-	inode = cb->inode;
-	btrfs_record_physical_zoned(inode, cb->start, bio);
 	btrfs_writepage_endio_finish_ordered(BTRFS_I(inode), NULL,
 			cb->start, cb->start + cb->len - 1,
-			bio->bi_status == BLK_STS_OK);
+			!cb->errors);
 
 	end_compressed_writeback(inode, cb);
-	/* note, our inode could be gone now */
+	/* Note, our inode could be gone now */
 
 	/*
-	 * release the compressed pages, these came from alloc_page and
+	 * Release the compressed pages, these came from alloc_page and
 	 * are not attached to the inode at all
 	 */
-	index = 0;
 	for (index = 0; index < cb->nr_pages; index++) {
-		page = cb->compressed_pages[index];
+		struct page *page = cb->compressed_pages[index];
+
 		page->mapping = NULL;
 		put_page(page);
 	}
 
-	/* finally free the cb struct */
+	/* Finally free the cb struct */
 	kfree(cb->compressed_pages);
 	kfree(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.
+ *
+ * This also calls the writeback end hooks for the file pages so that
+ * metadata and checksums can be updated in the file.
+ */
+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);
+
+	finish_compressed_bio_write(cb);
 out:
 	bio_put(bio);
 }
@@ -508,18 +514,18 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 			atomic_inc(&cb->pending_bios);
 			ret = btrfs_bio_wq_end_io(fs_info, bio,
 						  BTRFS_WQ_ENDIO_DATA);
-			BUG_ON(ret); /* -ENOMEM */
+			if (ret)
+				goto finish_cb;
 
 			if (!skip_sum) {
 				ret = btrfs_csum_one_bio(inode, bio, start, 1);
-				BUG_ON(ret); /* -ENOMEM */
+				if (ret)
+					goto finish_cb;
 			}
 
 			ret = btrfs_map_bio(fs_info, bio, 0);
-			if (ret) {
-				bio->bi_status = ret;
-				bio_endio(bio);
-			}
+			if (ret)
+				goto finish_cb;
 
 			bio = btrfs_bio_alloc(first_byte);
 			bio->bi_opf = bio_op | write_flags;
@@ -545,23 +551,44 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 
 	atomic_inc(&cb->pending_bios);
 	ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA);
-	BUG_ON(ret); /* -ENOMEM */
+	if (ret)
+		goto last_bio;
 
 	if (!skip_sum) {
 		ret = btrfs_csum_one_bio(inode, bio, start, 1);
-		BUG_ON(ret); /* -ENOMEM */
+		if (ret)
+			goto last_bio;
 	}
 
 	ret = btrfs_map_bio(fs_info, bio, 0);
-	if (ret) {
-		bio->bi_status = ret;
-		bio_endio(bio);
-	}
+	if (ret)
+		goto last_bio;
 
 	if (blkcg_css)
 		kthread_associate_blkcg(NULL);
 
 	return 0;
+last_bio:
+	bio->bi_status = ret;
+	/* One of the bios' endio function will free @cb. */
+	bio_endio(bio);
+	return ret;
+
+finish_cb:
+	if (bio) {
+		bio->bi_status = ret;
+		bio_endio(bio);
+	}
+
+	wait_var_event(cb, atomic_read(&cb->pending_bios) == 0);
+	/*
+	 * Even with previous bio ended, we should still have io not yet
+	 * submitted, thus need to finish manually.
+	 */
+	ASSERT(refcount_read(&cb->pending_sectors));
+	/* Now we are the only one referring @cb, can finish it safely. */
+	finish_compressed_bio_write(cb);
+	return ret;
 }
 
 static u64 bio_end_offset(struct bio *bio)
-- 
2.32.0

[PATCH v4 5/9] btrfs: introduce submit_compressed_bio() for compression

[Qu Wenruo]

The new helper, submit_compressed_bio(), will aggregate the following
work:

- Increase compressed_bio::pending_bios
- Remap the endio function
- Map and submit the bio

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/compression.c | 45 ++++++++++++++++++------------------------
 1 file changed, 19 insertions(+), 26 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index a88aee331022..19da5b26359b 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -416,6 +416,21 @@ static void end_compressed_bio_write(struct bio *bio)
 	bio_put(bio);
 }
 
+static blk_status_t submit_compressed_bio(struct btrfs_fs_info *fs_info,
+					  struct compressed_bio *cb,
+					  struct bio *bio, int mirror_num)
+{
+	blk_status_t ret;
+
+	ASSERT(bio->bi_iter.bi_size);
+	atomic_inc(&cb->pending_bios);
+	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;
+}
+
 /*
  * worker function to build and submit bios for previously compressed pages.
  * The corresponding pages in the inode should be marked for writeback
@@ -511,19 +526,13 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 
 		page->mapping = NULL;
 		if (submit || len < PAGE_SIZE) {
-			atomic_inc(&cb->pending_bios);
-			ret = btrfs_bio_wq_end_io(fs_info, bio,
-						  BTRFS_WQ_ENDIO_DATA);
-			if (ret)
-				goto finish_cb;
-
 			if (!skip_sum) {
 				ret = btrfs_csum_one_bio(inode, bio, start, 1);
 				if (ret)
 					goto finish_cb;
 			}
 
-			ret = btrfs_map_bio(fs_info, bio, 0);
+			ret = submit_compressed_bio(fs_info, cb, bio, 0);
 			if (ret)
 				goto finish_cb;
 
@@ -549,18 +558,13 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 		cond_resched();
 	}
 
-	atomic_inc(&cb->pending_bios);
-	ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA);
-	if (ret)
-		goto last_bio;
-
 	if (!skip_sum) {
 		ret = btrfs_csum_one_bio(inode, bio, start, 1);
 		if (ret)
 			goto last_bio;
 	}
 
-	ret = btrfs_map_bio(fs_info, bio, 0);
+	ret = submit_compressed_bio(fs_info, cb, bio, 0);
 	if (ret)
 		goto last_bio;
 
@@ -829,12 +833,6 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 		if (submit || bio_add_page(comp_bio, page, pg_len, 0) < pg_len) {
 			unsigned int nr_sectors;
 
-			atomic_inc(&cb->pending_bios);
-			ret = btrfs_bio_wq_end_io(fs_info, comp_bio,
-						  BTRFS_WQ_ENDIO_DATA);
-			if (ret)
-				goto finish_cb;
-
 			ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
 			if (ret)
 				goto finish_cb;
@@ -843,7 +841,7 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 						  fs_info->sectorsize);
 			sums += fs_info->csum_size * nr_sectors;
 
-			ret = btrfs_map_bio(fs_info, comp_bio, mirror_num);
+			ret = submit_compressed_bio(fs_info, cb, comp_bio, mirror_num);
 			if (ret)
 				goto finish_cb;
 
@@ -857,16 +855,11 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 		cur_disk_byte += pg_len;
 	}
 
-	atomic_inc(&cb->pending_bios);
-	ret = btrfs_bio_wq_end_io(fs_info, comp_bio, BTRFS_WQ_ENDIO_DATA);
-	if (ret)
-		goto last_bio;
-
 	ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
 	if (ret)
 		goto last_bio;
 
-	ret = btrfs_map_bio(fs_info, comp_bio, mirror_num);
+	ret = submit_compressed_bio(fs_info, cb, comp_bio, mirror_num);
 	if (ret)
 		goto last_bio;
 
-- 
2.32.0

[PATCH v4 6/9] btrfs: introduce alloc_compressed_bio() for compression

[Qu Wenruo]

Just aggregate the bio allocation code into one helper, so that we can
replace 4 call sites.

There is one special note for zoned write.

Currently btrfs_submit_compressed_write() will only allocate the first
bio using ZONE_APPEND.
If we have to submit current bio due to stripe boundary, the new bio
allocated will not use ZONE_APPEND.

In theory this should be a bug, but considering zoned mode currently
only support SINGLE profile, which doesn't have any stripe boundary
limit, it should never be a problem.

This function will provide a good entrance for any work which needs to be
done at bio allocation time. Like determining the stripe boundary.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/compression.c | 85 ++++++++++++++++++++++++++++--------------
 1 file changed, 57 insertions(+), 28 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 19da5b26359b..61c455ad1d60 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -431,6 +431,35 @@ static blk_status_t submit_compressed_bio(struct btrfs_fs_info *fs_info,
 	return ret;
 }
 
+/*
+ * To allocate a compressed_bio, which will be used to read/write on-disk data.
+ */
+static struct bio *alloc_compressed_bio(struct compressed_bio *cb, u64 disk_bytenr,
+					unsigned int opf, bio_end_io_t endio_func)
+{
+	struct bio *bio;
+
+	bio = btrfs_bio_alloc(disk_bytenr);
+
+	bio->bi_opf = opf;
+	bio->bi_private = cb;
+	bio->bi_end_io = endio_func;
+
+	if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
+		struct btrfs_fs_info *fs_info = btrfs_sb(cb->inode->i_sb);
+		struct btrfs_device *device;
+
+		device = btrfs_zoned_get_device(fs_info, disk_bytenr,
+						fs_info->sectorsize);
+		if (IS_ERR(device)) {
+			bio_put(bio);
+			return ERR_CAST(device);
+		}
+		bio_set_dev(bio, device->bdev);
+	}
+	return bio;
+}
+
 /*
  * worker function to build and submit bios for previously compressed pages.
  * The corresponding pages in the inode should be marked for writeback
@@ -477,22 +506,11 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 	cb->orig_bio = NULL;
 	cb->nr_pages = nr_pages;
 
-	bio = btrfs_bio_alloc(first_byte);
-	bio->bi_opf = bio_op | write_flags;
-	bio->bi_private = cb;
-	bio->bi_end_io = end_compressed_bio_write;
-
-	if (use_append) {
-		struct btrfs_device *device;
-
-		device = btrfs_zoned_get_device(fs_info, disk_start, PAGE_SIZE);
-		if (IS_ERR(device)) {
-			kfree(cb);
-			bio_put(bio);
-			return BLK_STS_NOTSUPP;
-		}
-
-		bio_set_dev(bio, device->bdev);
+	bio = alloc_compressed_bio(cb, first_byte, bio_op | write_flags,
+				   end_compressed_bio_write);
+	if (IS_ERR(bio)) {
+		kfree(cb);
+		return errno_to_blk_status(PTR_ERR(bio));
 	}
 
 	if (blkcg_css) {
@@ -536,10 +554,14 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 			if (ret)
 				goto finish_cb;
 
-			bio = btrfs_bio_alloc(first_byte);
-			bio->bi_opf = bio_op | write_flags;
-			bio->bi_private = cb;
-			bio->bi_end_io = end_compressed_bio_write;
+			bio = alloc_compressed_bio(cb, first_byte,
+					bio_op | write_flags,
+					end_compressed_bio_write);
+			if (IS_ERR(bio)) {
+				ret = errno_to_blk_status(PTR_ERR(bio));
+				bio = NULL;
+				goto finish_cb;
+			}
 			if (blkcg_css)
 				bio->bi_opf |= REQ_CGROUP_PUNT;
 			/*
@@ -801,10 +823,13 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	/* include any pages we added in add_ra-bio_pages */
 	cb->len = bio->bi_iter.bi_size;
 
-	comp_bio = btrfs_bio_alloc(cur_disk_byte);
-	comp_bio->bi_opf = REQ_OP_READ;
-	comp_bio->bi_private = cb;
-	comp_bio->bi_end_io = end_compressed_bio_read;
+	comp_bio = alloc_compressed_bio(cb, cur_disk_byte, REQ_OP_READ,
+					end_compressed_bio_read);
+	if (IS_ERR(comp_bio)) {
+		ret = errno_to_blk_status(PTR_ERR(comp_bio));
+		comp_bio = NULL;
+		goto fail2;
+	}
 
 	for (pg_index = 0; pg_index < nr_pages; pg_index++) {
 		u32 pg_len = PAGE_SIZE;
@@ -845,10 +870,14 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 			if (ret)
 				goto finish_cb;
 
-			comp_bio = btrfs_bio_alloc(cur_disk_byte);
-			comp_bio->bi_opf = REQ_OP_READ;
-			comp_bio->bi_private = cb;
-			comp_bio->bi_end_io = end_compressed_bio_read;
+			comp_bio = alloc_compressed_bio(cb, cur_disk_byte,
+					REQ_OP_READ,
+					end_compressed_bio_read);
+			if (IS_ERR(comp_bio)) {
+				ret = errno_to_blk_status(PTR_ERR(comp_bio));
+				comp_bio = NULL;
+				goto finish_cb;
+			}
 
 			bio_add_page(comp_bio, page, pg_len, 0);
 		}
-- 
2.32.0

[PATCH v4 7/9] btrfs: make btrfs_submit_compressed_read() to determine stripe boundary at bio allocation time

[Qu Wenruo]

Currently btrfs_submit_compressed_read() will check
btrfs_bio_fits_in_stripe() each time a new page is going to be added.

Even compressed extent is small, we don't really need to do that for
every page.

This patch will align the behavior to extent_io.c, by determining the
stripe boundary when allocating a bio.

Unlike extent_io.c, in compressed.c we don't need to bother things like
different bio flags, thus no need to re-use bio_ctrl.

Here we just manually introduce new local variable, next_stripe_start,
and teach alloc_compressed_bio() to calculate the stripe boundary.

Then each time we add some page range into the bio, we check if we
reached the boundary.
And if reached, submit it.

Also, since we have @cur_disk_byte to determine whether we're the last
bio, we don't need a explicit last_bio: tag for error handling any more.

And we can use @cur_disk_byte to track which range has been added to
bio, we can also use @cur_disk_byte to calculate the wait condition, no
need for @pending_bios.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/compression.c | 164 +++++++++++++++++++++++------------------
 1 file changed, 93 insertions(+), 71 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 61c455ad1d60..efe4ca3a9c6a 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -433,11 +433,18 @@ static blk_status_t submit_compressed_bio(struct btrfs_fs_info *fs_info,
 
 /*
  * To allocate a compressed_bio, which will be used to read/write on-disk data.
+ *
+ * @next_stripe_start:	Disk bytenr of next stripe start
  */
 static struct bio *alloc_compressed_bio(struct compressed_bio *cb, u64 disk_bytenr,
-					unsigned int opf, bio_end_io_t endio_func)
+					unsigned int opf, bio_end_io_t endio_func,
+					u64 *next_stripe_start)
 {
+	struct btrfs_fs_info *fs_info = btrfs_sb(cb->inode->i_sb);
+	struct btrfs_io_geometry geom;
+	struct extent_map *em;
 	struct bio *bio;
+	int ret;
 
 	bio = btrfs_bio_alloc(disk_bytenr);
 
@@ -445,18 +452,24 @@ static struct bio *alloc_compressed_bio(struct compressed_bio *cb, u64 disk_byte
 	bio->bi_private = cb;
 	bio->bi_end_io = endio_func;
 
-	if (bio_op(bio) == REQ_OP_ZONE_APPEND) {
-		struct btrfs_fs_info *fs_info = btrfs_sb(cb->inode->i_sb);
-		struct btrfs_device *device;
+	em = btrfs_get_chunk_map(fs_info, disk_bytenr, fs_info->sectorsize);
+	if (IS_ERR(em)) {
+		bio_put(bio);
+		return ERR_CAST(em);
+	}
 
-		device = btrfs_zoned_get_device(fs_info, disk_bytenr,
-						fs_info->sectorsize);
-		if (IS_ERR(device)) {
-			bio_put(bio);
-			return ERR_CAST(device);
-		}
-		bio_set_dev(bio, device->bdev);
+	if (bio_op(bio) == REQ_OP_ZONE_APPEND)
+		bio_set_dev(bio, em->map_lookup->stripes[0].dev->bdev);
+
+	ret = btrfs_get_io_geometry(fs_info, em, btrfs_op(bio), disk_bytenr,
+				    &geom);
+	free_extent_map(em);
+	if (ret < 0) {
+		bio_put(bio);
+		return ERR_PTR(ret);
 	}
+	*next_stripe_start = disk_bytenr + geom.len;
+
 	return bio;
 }
 
@@ -484,6 +497,7 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 	int pg_index = 0;
 	struct page *page;
 	u64 first_byte = disk_start;
+	u64 next_stripe_start;
 	blk_status_t ret;
 	int skip_sum = inode->flags & BTRFS_INODE_NODATASUM;
 	const bool use_append = btrfs_use_zone_append(inode, disk_start);
@@ -507,7 +521,8 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 	cb->nr_pages = nr_pages;
 
 	bio = alloc_compressed_bio(cb, first_byte, bio_op | write_flags,
-				   end_compressed_bio_write);
+				   end_compressed_bio_write,
+				   &next_stripe_start);
 	if (IS_ERR(bio)) {
 		kfree(cb);
 		return errno_to_blk_status(PTR_ERR(bio));
@@ -556,7 +571,8 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 
 			bio = alloc_compressed_bio(cb, first_byte,
 					bio_op | write_flags,
-					end_compressed_bio_write);
+					end_compressed_bio_write,
+					&next_stripe_start);
 			if (IS_ERR(bio)) {
 				ret = errno_to_blk_status(PTR_ERR(bio));
 				bio = NULL;
@@ -754,9 +770,10 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	unsigned int compressed_len;
 	unsigned int nr_pages;
 	unsigned int pg_index;
-	struct page *page;
-	struct bio *comp_bio;
-	u64 cur_disk_byte = bio->bi_iter.bi_sector << 9;
+	struct bio *comp_bio = NULL;
+	const u64 disk_bytenr = bio->bi_iter.bi_sector << SECTOR_SHIFT;
+	u64 cur_disk_byte = disk_bytenr;
+	u64 next_stripe_start;
 	u64 em_len;
 	u64 em_start;
 	struct extent_map *em;
@@ -823,39 +840,62 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	/* include any pages we added in add_ra-bio_pages */
 	cb->len = bio->bi_iter.bi_size;
 
-	comp_bio = alloc_compressed_bio(cb, cur_disk_byte, REQ_OP_READ,
-					end_compressed_bio_read);
-	if (IS_ERR(comp_bio)) {
-		ret = errno_to_blk_status(PTR_ERR(comp_bio));
-		comp_bio = NULL;
-		goto fail2;
-	}
-
-	for (pg_index = 0; pg_index < nr_pages; pg_index++) {
-		u32 pg_len = PAGE_SIZE;
-		int submit = 0;
+	while (cur_disk_byte < disk_bytenr + compressed_len) {
+		u64 offset = cur_disk_byte - disk_bytenr;
+		unsigned int index = offset >> PAGE_SHIFT;
+		unsigned int real_size;
+		unsigned int added;
+		struct page *page = cb->compressed_pages[index];
+		bool submit = false;
 
+		/* Allocate new bio if submitted or not yet allocated */
+		if (!comp_bio) {
+			comp_bio = alloc_compressed_bio(cb, cur_disk_byte,
+					REQ_OP_READ, end_compressed_bio_read,
+					&next_stripe_start);
+			if (IS_ERR(comp_bio)) {
+				ret = errno_to_blk_status(PTR_ERR(comp_bio));
+				comp_bio = NULL;
+				goto finish_cb;
+			}
+		}
 		/*
-		 * To handle subpage case, we need to make sure the bio only
-		 * covers the range we need.
-		 *
-		 * If we're at the last page, truncate the length to only cover
-		 * the remaining part.
+		 * We should never reach next_stripe_start start as we will
+		 * submit comp_bio when reach the boundary immediately.
+		 */
+		ASSERT(cur_disk_byte != next_stripe_start);
+		/*
+		 * We have various limit on the real read size:
+		 * - stripe boundary
+		 * - page boundary
+		 * - compressed length boundary
+		 */
+		real_size = min_t(u64, U32_MAX,
+				  next_stripe_start - cur_disk_byte);
+		real_size = min_t(u64, real_size,
+				  PAGE_SIZE - offset_in_page(offset));
+		real_size = min_t(u64, real_size,
+				  compressed_len - offset);
+		ASSERT(IS_ALIGNED(real_size, fs_info->sectorsize));
+
+		added = bio_add_page(comp_bio, page, real_size,
+				     offset_in_page(offset));
+		/*
+		 * Maximum compressed extent is smaller than bio size limit,
+		 * thus bio_add_page() should always success.
 		 */
-		if (pg_index == nr_pages - 1)
-			pg_len = min_t(u32, PAGE_SIZE,
-					compressed_len - pg_index * PAGE_SIZE);
+		ASSERT(added == real_size);
+		cur_disk_byte += added;
 
-		page = cb->compressed_pages[pg_index];
-		page->mapping = inode->i_mapping;
-		page->index = em_start >> PAGE_SHIFT;
+		/* Reached stripe boundary, need to submit */
+		if (cur_disk_byte == next_stripe_start)
+			submit = true;
 
-		if (comp_bio->bi_iter.bi_size)
-			submit = btrfs_bio_fits_in_stripe(page, pg_len,
-							  comp_bio, 0);
+		/* Has finished the range, need to submit */
+		if (cur_disk_byte == disk_bytenr + compressed_len)
+			submit = true;
 
-		page->mapping = NULL;
-		if (submit || bio_add_page(comp_bio, page, pg_len, 0) < pg_len) {
+		if (submit) {
 			unsigned int nr_sectors;
 
 			ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
@@ -866,32 +906,13 @@ blk_status_t 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, cb, comp_bio, mirror_num);
+			ret = submit_compressed_bio(fs_info, cb, comp_bio,
+						    mirror_num);
 			if (ret)
 				goto finish_cb;
-
-			comp_bio = alloc_compressed_bio(cb, cur_disk_byte,
-					REQ_OP_READ,
-					end_compressed_bio_read);
-			if (IS_ERR(comp_bio)) {
-				ret = errno_to_blk_status(PTR_ERR(comp_bio));
-				comp_bio = NULL;
-				goto finish_cb;
-			}
-
-			bio_add_page(comp_bio, page, pg_len, 0);
+			comp_bio = NULL;
 		}
-		cur_disk_byte += pg_len;
 	}
-
-	ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
-	if (ret)
-		goto last_bio;
-
-	ret = submit_compressed_bio(fs_info, cb, comp_bio, mirror_num);
-	if (ret)
-		goto last_bio;
-
 	return 0;
 
 fail2:
@@ -906,17 +927,18 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 out:
 	free_extent_map(em);
 	return ret;
-last_bio:
-	comp_bio->bi_status = ret;
-	/* This is the last bio, endio functions will free @cb */
-	bio_endio(comp_bio);
-	return ret;
 finish_cb:
 	if (comp_bio) {
 		comp_bio->bi_status = ret;
 		bio_endio(comp_bio);
 	}
-	wait_var_event(cb, atomic_read(&cb->pending_bios) == 0);
+	/* All bytes of @cb is submitted, endio will free @cb */
+	if (cur_disk_byte == disk_bytenr + compressed_len)
+		return ret;
+
+	wait_var_event(cb, refcount_read(&cb->pending_sectors) ==
+			   (disk_bytenr + compressed_len - cur_disk_byte) >>
+			   fs_info->sectorsize_bits);
 	/*
 	 * Even with previous bio ended, we should still have io not yet
 	 * submitted, thus need to finish @cb manually.
-- 
2.32.0

[PATCH v4 8/9] btrfs: make btrfs_submit_compressed_write() to determine stripe boundary at bio allocation time

[Qu Wenruo]

Currently btrfs_submit_compressed_write() will check
btrfs_bio_fits_in_stripe() each time a new page is going to be added.

Even compressed extent is small, we don't really need to do that for
every page.

This patch will align the behavior to extent_io.c, by determining the
stripe boundary when allocating a bio.

Unlike extent_io.c, in compressed.c we don't need to bother things like
different bio flags, thus no need to re-use bio_ctrl.

Here we just manually introduce new local variable, next_stripe_start,
and use that value returned from alloc_compressed_bio() to calculate
the stripe boundary.

Then each time we add some page range into the bio, we check if we
reached the boundary.
And if reached, submit it.

Also, since we have @cur_disk_bytenr to determine whether we're the last
bio, we don't need a explicit last_bio: tag for error handling any more.

And since we use @cur_disk_bytenr to wait, there is no need for
pending_bios, also remove it to save some memory of compressed_bio.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/compression.c | 145 ++++++++++++++++++-----------------------
 fs/btrfs/compression.h |   3 -
 2 files changed, 62 insertions(+), 86 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index efe4ca3a9c6a..b5487c80d2b6 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -222,7 +222,6 @@ static bool dec_and_test_compressed_bio(struct compressed_bio *cb,
 	ASSERT(bi_size && bi_size <= cb->compressed_len);
 	last_io = refcount_sub_and_test(bi_size >> fs_info->sectorsize_bits,
 					&cb->pending_sectors);
-	atomic_dec(&cb->pending_bios);
 	/*
 	 * Here we must wake up the possible error handler after all other
 	 * operations on @cb finished, or we can race with
@@ -423,7 +422,6 @@ static blk_status_t submit_compressed_bio(struct btrfs_fs_info *fs_info,
 	blk_status_t ret;
 
 	ASSERT(bio->bi_iter.bi_size);
-	atomic_inc(&cb->pending_bios);
 	ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA);
 	if (ret)
 		return ret;
@@ -493,10 +491,7 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 	struct btrfs_fs_info *fs_info = inode->root->fs_info;
 	struct bio *bio = NULL;
 	struct compressed_bio *cb;
-	unsigned long bytes_left;
-	int pg_index = 0;
-	struct page *page;
-	u64 first_byte = disk_start;
+	u64 cur_disk_bytenr = disk_start;
 	u64 next_stripe_start;
 	blk_status_t ret;
 	int skip_sum = inode->flags & BTRFS_INODE_NODATASUM;
@@ -507,7 +502,6 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 	cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS);
 	if (!cb)
 		return BLK_STS_RESOURCE;
-	atomic_set(&cb->pending_bios, 0);
 	refcount_set(&cb->pending_sectors,
 		     compressed_len >> fs_info->sectorsize_bits);
 	cb->errors = 0;
@@ -520,45 +514,65 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 	cb->orig_bio = NULL;
 	cb->nr_pages = nr_pages;
 
-	bio = alloc_compressed_bio(cb, first_byte, bio_op | write_flags,
-				   end_compressed_bio_write,
-				   &next_stripe_start);
-	if (IS_ERR(bio)) {
-		kfree(cb);
-		return errno_to_blk_status(PTR_ERR(bio));
-	}
-
-	if (blkcg_css) {
-		bio->bi_opf |= REQ_CGROUP_PUNT;
-		kthread_associate_blkcg(blkcg_css);
-	}
-
-	/* create and submit bios for the compressed pages */
-	bytes_left = compressed_len;
-	for (pg_index = 0; pg_index < cb->nr_pages; pg_index++) {
-		int submit = 0;
-		int len = 0;
+	while (cur_disk_bytenr < disk_start + compressed_len) {
+		u64 offset = cur_disk_bytenr - disk_start;
+		unsigned int index = offset >> PAGE_SHIFT;
+		unsigned int real_size;
+		unsigned int added;
+		struct page *page = compressed_pages[index];
+		bool submit = false;
 
-		page = compressed_pages[pg_index];
-		page->mapping = inode->vfs_inode.i_mapping;
-		if (bio->bi_iter.bi_size)
-			submit = btrfs_bio_fits_in_stripe(page, PAGE_SIZE, bio,
-							  0);
+		/* Allocate new bio if submitted or not yet allocated */
+		if (!bio) {
+			bio = alloc_compressed_bio(cb, cur_disk_bytenr,
+				bio_op | write_flags, end_compressed_bio_write,
+				&next_stripe_start);
+			if (IS_ERR(bio)) {
+				ret = errno_to_blk_status(PTR_ERR(bio));
+				bio = NULL;
+				goto finish_cb;
+			}
+		}
+		/*
+		 * We should never reach next_stripe_start start as we will
+		 * submit comp_bio when reach the boundary immediately.
+		 */
+		ASSERT(cur_disk_bytenr != next_stripe_start);
 
 		/*
-		 * Page can only be added to bio if the current bio fits in
-		 * stripe.
+		 * We have various limit on the real read size:
+		 * - stripe boundary
+		 * - page boundary
+		 * - compressed length boundary
 		 */
-		if (!submit) {
-			if (pg_index == 0 && use_append)
-				len = bio_add_zone_append_page(bio, page,
-							       PAGE_SIZE, 0);
-			else
-				len = bio_add_page(bio, page, PAGE_SIZE, 0);
-		}
+		real_size = min_t(u64, U32_MAX,
+				  next_stripe_start - cur_disk_bytenr);
+		real_size = min_t(u64, real_size,
+				  PAGE_SIZE - offset_in_page(offset));
+		real_size = min_t(u64, real_size,
+				  compressed_len - offset);
+		ASSERT(IS_ALIGNED(real_size, fs_info->sectorsize));
 
-		page->mapping = NULL;
-		if (submit || len < PAGE_SIZE) {
+		if (use_append)
+			added = bio_add_zone_append_page(bio, page, real_size,
+					offset_in_page(offset));
+		else
+			added = bio_add_page(bio, page, real_size,
+					offset_in_page(offset));
+		/* Reached zoned boundary */
+		if (added == 0)
+			submit = true;
+
+		cur_disk_bytenr += added;
+		/* Reached stripe boundary */
+		if (cur_disk_bytenr == next_stripe_start)
+			submit = true;
+
+		/* Finished the range */
+		if (cur_disk_bytenr == disk_start + compressed_len)
+			submit = true;
+
+		if (submit) {
 			if (!skip_sum) {
 				ret = btrfs_csum_one_bio(inode, bio, start, 1);
 				if (ret)
@@ -568,61 +582,27 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
 			ret = submit_compressed_bio(fs_info, cb, bio, 0);
 			if (ret)
 				goto finish_cb;
-
-			bio = alloc_compressed_bio(cb, first_byte,
-					bio_op | write_flags,
-					end_compressed_bio_write,
-					&next_stripe_start);
-			if (IS_ERR(bio)) {
-				ret = errno_to_blk_status(PTR_ERR(bio));
-				bio = NULL;
-				goto finish_cb;
-			}
-			if (blkcg_css)
-				bio->bi_opf |= REQ_CGROUP_PUNT;
-			/*
-			 * Use bio_add_page() to ensure the bio has at least one
-			 * page.
-			 */
-			bio_add_page(bio, page, PAGE_SIZE, 0);
-		}
-		if (bytes_left < PAGE_SIZE) {
-			btrfs_info(fs_info,
-					"bytes left %lu compress len %u nr %u",
-			       bytes_left, cb->compressed_len, cb->nr_pages);
+			bio = NULL;
 		}
-		bytes_left -= PAGE_SIZE;
-		first_byte += PAGE_SIZE;
 		cond_resched();
 	}
-
-	if (!skip_sum) {
-		ret = btrfs_csum_one_bio(inode, bio, start, 1);
-		if (ret)
-			goto last_bio;
-	}
-
-	ret = submit_compressed_bio(fs_info, cb, bio, 0);
-	if (ret)
-		goto last_bio;
-
 	if (blkcg_css)
 		kthread_associate_blkcg(NULL);
 
 	return 0;
-last_bio:
-	bio->bi_status = ret;
-	/* One of the bios' endio function will free @cb. */
-	bio_endio(bio);
-	return ret;
 
 finish_cb:
 	if (bio) {
 		bio->bi_status = ret;
 		bio_endio(bio);
 	}
+	/* Last byte of @cb is submitted, endio will free @cb */
+	if (cur_disk_bytenr == disk_start + compressed_len)
+		return ret;
 
-	wait_var_event(cb, atomic_read(&cb->pending_bios) == 0);
+	wait_var_event(cb, refcount_read(&cb->pending_sectors) ==
+			   (disk_start + compressed_len - cur_disk_bytenr) >>
+			   fs_info->sectorsize_bits);
 	/*
 	 * Even with previous bio ended, we should still have io not yet
 	 * submitted, thus need to finish manually.
@@ -797,7 +777,6 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	if (!cb)
 		goto out;
 
-	atomic_set(&cb->pending_bios, 0);
 	refcount_set(&cb->pending_sectors,
 		     compressed_len >> fs_info->sectorsize_bits);
 	cb->errors = 0;
diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
index 8940e9e9fed3..2490de810cd8 100644
--- a/fs/btrfs/compression.h
+++ b/fs/btrfs/compression.h
@@ -28,9 +28,6 @@ struct btrfs_inode;
 #define	BTRFS_ZLIB_DEFAULT_LEVEL		3
 
 struct compressed_bio {
-	/* number of bios pending for this compressed extent */
-	atomic_t pending_bios;
-
 	/* Number of sectors with unfinished IO (unsubmitted or unfinished) */
 	refcount_t pending_sectors;
 
-- 
2.32.0

[PATCH v4 9/9] btrfs: remove unused function btrfs_bio_fits_in_stripe()

[Qu Wenruo]

As the last caller in compression.c is removed, we don't need that
function anymore.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/ctree.h |  2 --
 fs/btrfs/inode.c | 42 ------------------------------------------
 2 files changed, 44 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 2fbd5330e2da..f33812c68454 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3163,8 +3163,6 @@ void btrfs_merge_delalloc_extent(struct inode *inode, struct extent_state *new,
 				 struct extent_state *other);
 void btrfs_split_delalloc_extent(struct inode *inode,
 				 struct extent_state *orig, u64 split);
-int btrfs_bio_fits_in_stripe(struct page *page, size_t size, struct bio *bio,
-			     unsigned long bio_flags);
 void btrfs_set_range_writeback(struct btrfs_inode *inode, u64 start, u64 end);
 vm_fault_t btrfs_page_mkwrite(struct vm_fault *vmf);
 int btrfs_readpage(struct file *file, struct page *page);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 19421cde2050..987187c4dd72 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2217,48 +2217,6 @@ void btrfs_clear_delalloc_extent(struct inode *vfs_inode,
 	}
 }
 
-/*
- * btrfs_bio_fits_in_stripe - Checks whether the size of the given bio will fit
- * in a chunk's stripe. This function ensures that bios do not span a
- * stripe/chunk
- *
- * @page - The page we are about to add to the bio
- * @size - size we want to add to the bio
- * @bio - bio we want to ensure is smaller than a stripe
- * @bio_flags - flags of the bio
- *
- * return 1 if page cannot be added to the bio
- * return 0 if page can be added to the bio
- * return error otherwise
- */
-int btrfs_bio_fits_in_stripe(struct page *page, size_t size, struct bio *bio,
-			     unsigned long bio_flags)
-{
-	struct inode *inode = page->mapping->host;
-	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
-	u64 logical = bio->bi_iter.bi_sector << 9;
-	u32 bio_len = bio->bi_iter.bi_size;
-	struct extent_map *em;
-	int ret = 0;
-	struct btrfs_io_geometry geom;
-
-	if (bio_flags & EXTENT_BIO_COMPRESSED)
-		return 0;
-
-	em = btrfs_get_chunk_map(fs_info, logical, fs_info->sectorsize);
-	if (IS_ERR(em))
-		return PTR_ERR(em);
-	ret = btrfs_get_io_geometry(fs_info, em, btrfs_op(bio), logical, &geom);
-	if (ret < 0)
-		goto out;
-
-	if (geom.len < bio_len + size)
-		ret = 1;
-out:
-	free_extent_map(em);
-	return 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
-- 
2.32.0

Re: [PATCH v4 0/9] btrfs: compression: refactor and enhancement preparing for subpage compression support

[David Sterba]

On Thu, Jun 17, 2021 at 01:14:41PM +0800, Qu Wenruo wrote:
> There are quite some problems in compression code:
> 
> - Weird compressed_bio::pending_bios dance
>   If we just don't want compressed_bio being freed halfway, we have more
>   sane methods, just like btrfs_subpage::readers.
> 
>   So here we fix it by introducing compressed_bio::io_sectors to do the
>   job.
> 
> - BUG_ON()s inside btrfs_submit_compressed_*()
>   Even they are just ENOMEM, we should handle them.
>   With io_sectors introduced, we have a way to finish compressed_bio
>   all by ourselves, as long as we haven't submitted last bio.
> 
>   If we have last bio submitted, then endio will handle it well.
> 
> - Duplicated code for compressed bio allocation and submission
>   Just small refactor can handle it
> 
> - Stripe boundary is checked every time one page is added
>   This is overkilled.
>   Just learn from extent_io.c refactor which use bio_ctrl to do the
>   boundary check only once for each bio.
> 
>   Although in compression context, we don't need extra checks in
>   extent_io.c, thus we don't need bio_ctrl structure, but
>   can afford to do it locally.
> 
> - Dead code removal
>   One dead comment and a new zombie function,
>   btrfs_bio_fits_in_stripe(), can be removed now.

I went through it several times, the changes are scary, but the overall
direction is IMHO the right one, not to say it's fixing the difficult
BUG_ONs.

I'll put it to for-next once it passes a few rounds of fstests. Taking
it to 5.14 could be risky if we don't have enough review and testing,
time is almost up before the code freeze.

Re: [PATCH v4 0/9] btrfs: compression: refactor and enhancement preparing for subpage compression support

[Qu Wenruo]

On 2021/6/18 上午12:47, David Sterba wrote:
> On Thu, Jun 17, 2021 at 01:14:41PM +0800, Qu Wenruo wrote:
>> There are quite some problems in compression code:
>>
>> - Weird compressed_bio::pending_bios dance
>>    If we just don't want compressed_bio being freed halfway, we have more
>>    sane methods, just like btrfs_subpage::readers.
>>
>>    So here we fix it by introducing compressed_bio::io_sectors to do the
>>    job.
>>
>> - BUG_ON()s inside btrfs_submit_compressed_*()
>>    Even they are just ENOMEM, we should handle them.
>>    With io_sectors introduced, we have a way to finish compressed_bio
>>    all by ourselves, as long as we haven't submitted last bio.
>>
>>    If we have last bio submitted, then endio will handle it well.
>>
>> - Duplicated code for compressed bio allocation and submission
>>    Just small refactor can handle it
>>
>> - Stripe boundary is checked every time one page is added
>>    This is overkilled.
>>    Just learn from extent_io.c refactor which use bio_ctrl to do the
>>    boundary check only once for each bio.
>>
>>    Although in compression context, we don't need extra checks in
>>    extent_io.c, thus we don't need bio_ctrl structure, but
>>    can afford to do it locally.
>>
>> - Dead code removal
>>    One dead comment and a new zombie function,
>>    btrfs_bio_fits_in_stripe(), can be removed now.
>
> I went through it several times, the changes are scary, but the overall
> direction is IMHO the right one, not to say it's fixing the difficult
> BUG_ONs.
>
> I'll put it to for-next once it passes a few rounds of fstests. Taking
> it to 5.14 could be risky if we don't have enough review and testing,
> time is almost up before the code freeze.
>
Please don't put it into 5.14.

It's really a preparation for subpage compression support.
However we don't even have subpage queued for v5.14, thus I'm not in a
hurry.

Thanks,
Qu

Re: [PATCH v4 2/9] btrfs: introduce compressed_bio::pending_sectors to trace compressed bio more elegantly

[Anand Jain]

On 17/06/2021 13:14, Qu Wenruo wrote:
> For btrfs_submit_compressed_read() and btrfs_submit_compressed_write(),
> we have a pretty weird dance around compressed_bio::pending_bios:
> 
>    btrfs_submit_compressed_read/write()
>    {
> 	cb = kmalloc()
> 	refcount_set(&cb->pending_bios, 0);
> 	bio = btrfs_alloc_bio();
> 
> 	/* NOTE here, we haven't yet submitted any bio */
> 	refcount_set(&cb->pending_bios, 1);
> 
> 	for (pg_index = 0; pg_index < cb->nr_pages; pg_index++) {
> 		if (submit) {
> 			/* Here we submit bio, but we always have one
> 			 * extra pending_bios */
> 			refcount_inc(&cb->pending_bios);
> 			ret = btrfs_map_bio();
> 		}
> 	}
> 
> 	/* Submit the last bio */
> 	ret = btrfs_map_bio();
>    }
> 
> There are two reasons why we do this:
> 
> - compressed_bio::pending_bios is a refcount
>    Thus if it's reduced to 0, it can not be increased again.
> 
> - To ensure the compressed_bio is not freed by some submitted bios
>    If the submitted bio is finished before the next bio submitted,
>    we can free the compressed_bio completely.
> 
> But the above code is sometimes confusing, and we can do it better by
> just introduce a new member, compressed_bio::pending_sectors.
> 
> Now we use compressed_bio::pending_sectors to indicate whether we have any
> pending sectors under IO or not yet submitted.
> 
> If pending_sectors == 0, we're definitely the last bio of compressed_bio, and
> is OK to release the compressed bio.
> 
> Now the workflow looks like this:
> 
>    btrfs_submit_compressed_read/write()
>    {
> 	cb = kmalloc()
> 	atomic_set(&cb->pending_bios, 0);
> 	refcount_set(&cb->pending_sectors,
> 		     compressed_len >> sectorsize_bits);
> 	bio = btrfs_alloc_bio();
> 
> 	for (pg_index = 0; pg_index < cb->nr_pages; pg_index++) {
> 		if (submit) {
> 			refcount_inc(&cb->pending_bios);
> 			ret = btrfs_map_bio();
> 		}
> 	}
> 
> 	/* Submit the last bio */
> 	refcount_inc(&cb->pending_bios);
> 	ret = btrfs_map_bio();
>    }
> 
> For now we still need pending_bios for later error handling, but will
> remove pending_bios eventually after properly handling the errors.
> 
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>   fs/btrfs/compression.c | 78 ++++++++++++++++++++++++------------------
>   fs/btrfs/compression.h |  5 ++-
>   2 files changed, 49 insertions(+), 34 deletions(-)
> 
> diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
> index 9a023ae0f98b..b84b9f7420c2 100644
> --- a/fs/btrfs/compression.c
> +++ b/fs/btrfs/compression.c
> @@ -193,6 +193,39 @@ static int check_compressed_csum(struct btrfs_inode *inode, struct bio *bio,
>   	return 0;
>   }
>   
> +/*
> + * Reduce bio and io accounting for a compressed_bio with its coresponding bio.
> + *
> + * Return true if there is no pending bio nor io.
> + * Return false otherwise.
> + */
> +static bool dec_and_test_compressed_bio(struct compressed_bio *cb,
> +					struct bio *bio)
> +{
> +	struct btrfs_fs_info *fs_info = btrfs_sb(cb->inode->i_sb);
> +	unsigned int bi_size = 0;
> +	bool last_io = false;
> +	struct bio_vec *bvec;
> +	struct bvec_iter_all iter_all;
> +
> +	/*
> +	 * At endio time, bi_iter.bi_size doesn't represent the real bio size.
> +	 * Thus here we have to iterate through all segments to grab correct
> +	 * bio size.
> +	 */
> +	bio_for_each_segment_all(bvec, bio, iter_all)
> +		bi_size += bvec->bv_len;
> +
> +	if (bio->bi_status)
> +		cb->errors = 1;
> +
> +	ASSERT(bi_size && bi_size <= cb->compressed_len);
> +	last_io = refcount_sub_and_test(bi_size >> fs_info->sectorsize_bits,
> +					&cb->pending_sectors);
> +	atomic_dec(&cb->pending_bios);
> +	return last_io;
> +}
> +
>   /* when we finish reading compressed pages from the disk, we
>    * decompress them and then run the bio end_io routines on the
>    * decompressed pages (in the inode address space).
> @@ -212,13 +245,7 @@ static void end_compressed_bio_read(struct bio *bio)
>   	unsigned int mirror = btrfs_io_bio(bio)->mirror_num;
>   	int ret = 0;
>   
> -	if (bio->bi_status)
> -		cb->errors = 1;
> -
> -	/* if there are more bios still pending for this compressed
> -	 * extent, just exit
> -	 */
> -	if (!refcount_dec_and_test(&cb->pending_bios))
> +	if (!dec_and_test_compressed_bio(cb, bio))
>   		goto out;
>   
>   	/*
> @@ -336,13 +363,7 @@ static void end_compressed_bio_write(struct bio *bio)
>   	struct page *page;
>   	unsigned int index;
>   
> -	if (bio->bi_status)
> -		cb->errors = 1;
> -
> -	/* if there are more bios still pending for this compressed
> -	 * extent, just exit
> -	 */
> -	if (!refcount_dec_and_test(&cb->pending_bios))
> +	if (!dec_and_test_compressed_bio(cb, bio))
>   		goto out;
>   
>   	/* ok, we're the last bio for this extent, step one is to
> @@ -408,7 +429,9 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
>   	cb = kmalloc(compressed_bio_size(fs_info, compressed_len), GFP_NOFS);
>   	if (!cb)
>   		return BLK_STS_RESOURCE;
> -	refcount_set(&cb->pending_bios, 0);
> +	atomic_set(&cb->pending_bios, 0);
> +	refcount_set(&cb->pending_sectors,
> +		     compressed_len >> fs_info->sectorsize_bits);
>   	cb->errors = 0;
>   	cb->inode = &inode->vfs_inode;
>   	cb->start = start;
> @@ -441,7 +464,6 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
>   		bio->bi_opf |= REQ_CGROUP_PUNT;
>   		kthread_associate_blkcg(blkcg_css);
>   	}
> -	refcount_set(&cb->pending_bios, 1);
>   
>   	/* create and submit bios for the compressed pages */
>   	bytes_left = compressed_len;
> @@ -469,13 +491,7 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
>   
>   		page->mapping = NULL;
>   		if (submit || len < PAGE_SIZE) {
> -			/*
> -			 * inc the count before we submit the bio so
> -			 * we know the end IO handler won't happen before
> -			 * we inc the count.  Otherwise, the cb might get
> -			 * freed before we're done setting it up
> -			 */
> -			refcount_inc(&cb->pending_bios);
> +			atomic_inc(&cb->pending_bios);
>   			ret = btrfs_bio_wq_end_io(fs_info, bio,
>   						  BTRFS_WQ_ENDIO_DATA);
>   			BUG_ON(ret); /* -ENOMEM */
> @@ -513,6 +529,7 @@ blk_status_t btrfs_submit_compressed_write(struct btrfs_inode *inode, u64 start,
>   		cond_resched();
>   	}
>   
> +	atomic_inc(&cb->pending_bios);
>   	ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA);
>   	BUG_ON(ret); /* -ENOMEM */
>   
> @@ -696,7 +713,9 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
>   	if (!cb)
>   		goto out;
>   
> -	refcount_set(&cb->pending_bios, 0);
> +	atomic_set(&cb->pending_bios, 0);
> +	refcount_set(&cb->pending_sectors,
> +		     compressed_len >> fs_info->sectorsize_bits);
>   	cb->errors = 0;
>   	cb->inode = inode;
>   	cb->mirror_num = mirror_num;
> @@ -741,7 +760,6 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
>   	comp_bio->bi_opf = REQ_OP_READ;
>   	comp_bio->bi_private = cb;
>   	comp_bio->bi_end_io = end_compressed_bio_read;
> -	refcount_set(&cb->pending_bios, 1);
>   
>   	for (pg_index = 0; pg_index < nr_pages; pg_index++) {
>   		u32 pg_len = PAGE_SIZE;
> @@ -770,18 +788,11 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
>   		if (submit || bio_add_page(comp_bio, page, pg_len, 0) < pg_len) {
>   			unsigned int nr_sectors;
>   

> +			atomic_inc(&cb->pending_bios);
>   			ret = btrfs_bio_wq_end_io(fs_info, comp_bio,
>   						  BTRFS_WQ_ENDIO_DATA);
>   			BUG_ON(ret); /* -ENOMEM */
>   
> -			/*
> -			 * inc the count before we submit the bio so
> -			 * we know the end IO handler won't happen before
> -			 * we inc the count.  Otherwise, the cb might get
> -			 * freed before we're done setting it up
> -			 */
> -			refcount_inc(&cb->pending_bios);
> -

Looks good so far.
I understand pending_bios will go away in favour of pending_sectors.
But here, is there any purpose  atomic_inc(&cb->pending_bios) is called 
before btrfs_bio_wq_end_io() that might fail.

-Anand


>   			ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
>   			BUG_ON(ret); /* -ENOMEM */
>   
> @@ -805,6 +816,7 @@ blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
>   		cur_disk_byte += pg_len;
>   	}
>   
> +	atomic_inc(&cb->pending_bios);
>   	ret = btrfs_bio_wq_end_io(fs_info, comp_bio, BTRFS_WQ_ENDIO_DATA);
>   	BUG_ON(ret); /* -ENOMEM */
>   
> diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
> index c359f20920d0..8940e9e9fed3 100644
> --- a/fs/btrfs/compression.h
> +++ b/fs/btrfs/compression.h
> @@ -29,7 +29,10 @@ struct btrfs_inode;
>   
>   struct compressed_bio {
>   	/* number of bios pending for this compressed extent */
> -	refcount_t pending_bios;
> +	atomic_t pending_bios;
> +
> +	/* Number of sectors with unfinished IO (unsubmitted or unfinished) */
> +	refcount_t pending_sectors;
>   
>   	/* Number of compressed pages in the array */
>   	unsigned int nr_pages;
> 

Re: [PATCH v4 2/9] btrfs: introduce compressed_bio::pending_sectors to trace compressed bio more elegantly

[Qu Wenruo]

On 2021/6/18 下午12:16, Anand Jain wrote:
> On 17/06/2021 13:14, Qu Wenruo wrote:
[...]
> 
>> +            atomic_inc(&cb->pending_bios);
>>               ret = btrfs_bio_wq_end_io(fs_info, comp_bio,
>>                             BTRFS_WQ_ENDIO_DATA);
>>               BUG_ON(ret); /* -ENOMEM */
>> -            /*
>> -             * inc the count before we submit the bio so
>> -             * we know the end IO handler won't happen before
>> -             * we inc the count.  Otherwise, the cb might get
>> -             * freed before we're done setting it up
>> -             */
>> -            refcount_inc(&cb->pending_bios);
>> -
> 
> Looks good so far.
> I understand pending_bios will go away in favour of pending_sectors.
> But here, is there any purpose  atomic_inc(&cb->pending_bios) is called 
> before btrfs_bio_wq_end_io() that might fail.

The pending_bios is increased before we may want to submit the bio.

There is no special reason, but we will later merge refcount_inc();
btrfs_bio_wq_end_io(), btrfs_map_bio() into one call, thus I just choose
btrfs_bio_wq_end_io() as a marker.

Thanks,
Qu
> 
> -Anand
> 
> 
>>               ret = btrfs_lookup_bio_sums(inode, comp_bio, sums);
>>               BUG_ON(ret); /* -ENOMEM */
>> @@ -805,6 +816,7 @@ blk_status_t btrfs_submit_compressed_read(struct 
>> inode *inode, struct bio *bio,
>>           cur_disk_byte += pg_len;
>>       }
>> +    atomic_inc(&cb->pending_bios);
>>       ret = btrfs_bio_wq_end_io(fs_info, comp_bio, BTRFS_WQ_ENDIO_DATA);
>>       BUG_ON(ret); /* -ENOMEM */
>> diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
>> index c359f20920d0..8940e9e9fed3 100644
>> --- a/fs/btrfs/compression.h
>> +++ b/fs/btrfs/compression.h
>> @@ -29,7 +29,10 @@ struct btrfs_inode;
>>   struct compressed_bio {
>>       /* number of bios pending for this compressed extent */
>> -    refcount_t pending_bios;
>> +    atomic_t pending_bios;
>> +
>> +    /* Number of sectors with unfinished IO (unsubmitted or 
>> unfinished) */
>> +    refcount_t pending_sectors;
>>       /* Number of compressed pages in the array */
>>       unsigned int nr_pages;
>>
> 

Re: [PATCH v4 0/9] btrfs: compression: refactor and enhancement preparing for subpage compression support

[David Sterba]

On Fri, Jun 18, 2021 at 06:46:51AM +0800, Qu Wenruo wrote:
> > I went through it several times, the changes are scary, but the overall
> > direction is IMHO the right one, not to say it's fixing the difficult
> > BUG_ONs.
> >
> > I'll put it to for-next once it passes a few rounds of fstests. Taking
> > it to 5.14 could be risky if we don't have enough review and testing,
> > time is almost up before the code freeze.
> >
> Please don't put it into 5.14.
> 
> It's really a preparation for subpage compression support.
> However we don't even have subpage queued for v5.14, thus I'm not in a
> hurry.

Ok, no problem. As merge window is close I'll keep the compression and
subpage out of for-next until rc1 is out, the timestamped for-next
snapshots branches could contain it so we can start testing.

Re: [PATCH v4 0/9] btrfs: compression: refactor and enhancement preparing for subpage compression support

[Qu Wenruo]

On 2021/6/22 下午7:14, David Sterba wrote:
> On Fri, Jun 18, 2021 at 06:46:51AM +0800, Qu Wenruo wrote:
>>> I went through it several times, the changes are scary, but the overall
>>> direction is IMHO the right one, not to say it's fixing the difficult
>>> BUG_ONs.
>>>
>>> I'll put it to for-next once it passes a few rounds of fstests. Taking
>>> it to 5.14 could be risky if we don't have enough review and testing,
>>> time is almost up before the code freeze.
>>>
>> Please don't put it into 5.14.
>>
>> It's really a preparation for subpage compression support.
>> However we don't even have subpage queued for v5.14, thus I'm not in a
>> hurry.
>
> Ok, no problem. As merge window is close I'll keep the compression and
> subpage out of for-next until rc1 is out, the timestamped for-next
> snapshots branches could contain it so we can start testing.
>
Sounds great.

Although the biggest challenge for testing is the hardware.

I guess even with subpage merged into upstream in v5.14, it won't really
get many tests from real world, unlike x86_64 that every guys in the
mail list is testing on.

Although we have cheap ARM SoC boards in recent days, there aren't
really much good candidates for us to utilize.

Either they don't have fast enough CPUs (2x 2GHz+ A72 or more) or don't
have even a single PCIe lane for NVME, or don't have good enough
upstream kernel support.

So far RPI CM4 would be a pretty good candidate, and I'm already using
it, but without overclocking and good heatsink, its CPU can be a little
bit slow, and the PCIe2.0 x1 lane is far from enough.

But I totally understand how difficult it could be for even kernel
developers to setup all the small things up.

Like TTY, libvirt, edk2 firmware for VM, RPI specific boot sequence etc.

Thus even subpage get merged, I still think we need way more rounds of
upstream release to really get some feedback.

Thanks,
Qu

Re: [PATCH v4 0/9] btrfs: compression: refactor and enhancement preparing for subpage compression support

[David Sterba]

On Tue, Jun 22, 2021 at 07:50:38PM +0800, Qu Wenruo wrote:
> On 2021/6/22 下午7:14, David Sterba wrote:
> > On Fri, Jun 18, 2021 at 06:46:51AM +0800, Qu Wenruo wrote:
> Although the biggest challenge for testing is the hardware.
> 
> I guess even with subpage merged into upstream in v5.14, it won't really
> get many tests from real world, unlike x86_64 that every guys in the
> mail list is testing on.
> 
> Although we have cheap ARM SoC boards in recent days, there aren't
> really much good candidates for us to utilize.
> 
> Either they don't have fast enough CPUs (2x 2GHz+ A72 or more) or don't
> have even a single PCIe lane for NVME, or don't have good enough
> upstream kernel support.
> 
> So far RPI CM4 would be a pretty good candidate, and I'm already using
> it, but without overclocking and good heatsink, its CPU can be a little
> bit slow, and the PCIe2.0 x1 lane is far from enough.
> 
> But I totally understand how difficult it could be for even kernel
> developers to setup all the small things up.
> 
> Like TTY, libvirt, edk2 firmware for VM, RPI specific boot sequence etc.
> 
> Thus even subpage get merged, I still think we need way more rounds of
> upstream release to really get some feedback.

Back in January I got a hold of a decent arm64 machine and tested the 64K
build in a VM, the hardware should be good enough for running at least
3 in parallel and I think there were more identical physical machines
available so we can use that for testing once all the prep work is done.
Right now all people involved know that the subpage support may be buggy
or incomplete so we can rely on external testing for some time.