[PATCH 0/3 v2] Switch to on-stack variables for block reserves

[PATCH 0/3 v2] Switch to on-stack variables for block reserves

[David Sterba]

The block reserve structure is small enough to fit on stack so do that
in a few functions and avoid allocation.

v2:
- drop patch replacing allocated reserve in relocation, crash in btrfs/190
- v1 https://lore.kernel.org/linux-btrfs/cover.1695408280.git.dsterba@suse.com/

David Sterba (3):
  btrfs: use on-stack variable for block reserve in btrfs_evict_inode()
  btrfs: use on-stack variable for block reserve in btrfs_truncate()
  btrfs: use on-stack variable for block reserve in
    btrfs_replace_file_extents()

 fs/btrfs/file.c  | 29 ++++++++++++-----------------
 fs/btrfs/inode.c | 47 ++++++++++++++++++++++-------------------------
 2 files changed, 34 insertions(+), 42 deletions(-)

-- 
2.47.1

[PATCH 1/3] btrfs: use on-stack variable for block reserve in btrfs_evict_inode()

[David Sterba]

We can avoid potential memory allocation failure in btrfs_evict_inode()
as the block reserve lifetime is limited to the scope of the function.
This requires +48 bytes on stack.

Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/inode.c | 25 ++++++++++++-------------
 1 file changed, 12 insertions(+), 13 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index c297963f56bd..496194832166 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -5434,7 +5434,7 @@ void btrfs_evict_inode(struct inode *inode)
 	struct btrfs_fs_info *fs_info;
 	struct btrfs_trans_handle *trans;
 	struct btrfs_root *root = BTRFS_I(inode)->root;
-	struct btrfs_block_rsv *rsv = NULL;
+	struct btrfs_block_rsv rsv;
 	int ret;
 
 	trace_btrfs_inode_evict(inode);
@@ -5482,11 +5482,9 @@ void btrfs_evict_inode(struct inode *inode)
 	 */
 	btrfs_kill_delayed_inode_items(BTRFS_I(inode));
 
-	rsv = btrfs_alloc_block_rsv(fs_info, BTRFS_BLOCK_RSV_TEMP);
-	if (!rsv)
-		goto out;
-	rsv->size = btrfs_calc_metadata_size(fs_info, 1);
-	rsv->failfast = true;
+	btrfs_init_metadata_block_rsv(fs_info, &rsv, BTRFS_BLOCK_RSV_TEMP);
+	rsv.size = btrfs_calc_metadata_size(fs_info, 1);
+	rsv.failfast = true;
 
 	btrfs_i_size_write(BTRFS_I(inode), 0);
 
@@ -5498,11 +5496,11 @@ void btrfs_evict_inode(struct inode *inode)
 			.min_type = 0,
 		};
 
-		trans = evict_refill_and_join(root, rsv);
+		trans = evict_refill_and_join(root, &rsv);
 		if (IS_ERR(trans))
-			goto out;
+			goto out_release;
 
-		trans->block_rsv = rsv;
+		trans->block_rsv = &rsv;
 
 		ret = btrfs_truncate_inode_items(trans, root, &control);
 		trans->block_rsv = &fs_info->trans_block_rsv;
@@ -5514,7 +5512,7 @@ void btrfs_evict_inode(struct inode *inode)
 		 */
 		btrfs_btree_balance_dirty_nodelay(fs_info);
 		if (ret && ret != -ENOSPC && ret != -EAGAIN)
-			goto out;
+			goto out_release;
 		else if (!ret)
 			break;
 	}
@@ -5528,16 +5526,17 @@ void btrfs_evict_inode(struct inode *inode)
 	 * If it turns out that we are dropping too many of these, we might want
 	 * to add a mechanism for retrying these after a commit.
 	 */
-	trans = evict_refill_and_join(root, rsv);
+	trans = evict_refill_and_join(root, &rsv);
 	if (!IS_ERR(trans)) {
-		trans->block_rsv = rsv;
+		trans->block_rsv = &rsv;
 		btrfs_orphan_del(trans, BTRFS_I(inode));
 		trans->block_rsv = &fs_info->trans_block_rsv;
 		btrfs_end_transaction(trans);
 	}
 
+out_release:
+	btrfs_block_rsv_release(fs_info, &rsv, (u64)-1, NULL);
 out:
-	btrfs_free_block_rsv(fs_info, rsv);
 	/*
 	 * If we didn't successfully delete, the orphan item will still be in
 	 * the tree and we'll retry on the next mount. Again, we might also want
-- 
2.47.1

[PATCH 2/3] btrfs: use on-stack variable for block reserve in btrfs_truncate()

[David Sterba]

We can avoid potential memory allocation failure in btrfs_truncate() as
the block reserve lifetime is limited to the scope of the function. This
requires +48 bytes on stack.

Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/inode.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 496194832166..3976a90e3c3c 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7604,7 +7604,7 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
 	};
 	struct btrfs_root *root = inode->root;
 	struct btrfs_fs_info *fs_info = root->fs_info;
-	struct btrfs_block_rsv *rsv;
+	struct btrfs_block_rsv rsv;
 	int ret;
 	struct btrfs_trans_handle *trans;
 	u64 mask = fs_info->sectorsize - 1;
@@ -7646,11 +7646,9 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
 	 * 2) fs_info->trans_block_rsv - this will have 1 items worth left for
 	 * updating the inode.
 	 */
-	rsv = btrfs_alloc_block_rsv(fs_info, BTRFS_BLOCK_RSV_TEMP);
-	if (!rsv)
-		return -ENOMEM;
-	rsv->size = min_size;
-	rsv->failfast = true;
+	btrfs_init_metadata_block_rsv(fs_info, &rsv, BTRFS_BLOCK_RSV_TEMP);
+	rsv.size = min_size;
+	rsv.failfast = true;
 
 	/*
 	 * 1 for the truncate slack space
@@ -7663,7 +7661,7 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
 	}
 
 	/* Migrate the slack space for the truncate to our reserve */
-	ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv, rsv,
+	ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv, &rsv,
 				      min_size, false);
 	/*
 	 * We have reserved 2 metadata units when we started the transaction and
@@ -7675,7 +7673,7 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
 		goto out;
 	}
 
-	trans->block_rsv = rsv;
+	trans->block_rsv = &rsv;
 
 	while (1) {
 		struct extent_state *cached_state = NULL;
@@ -7718,9 +7716,9 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
 			break;
 		}
 
-		btrfs_block_rsv_release(fs_info, rsv, -1, NULL);
+		btrfs_block_rsv_release(fs_info, &rsv, -1, NULL);
 		ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv,
-					      rsv, min_size, false);
+					      &rsv, min_size, false);
 		/*
 		 * We have reserved 2 metadata units when we started the
 		 * transaction and min_size matches 1 unit, so this should never
@@ -7729,7 +7727,7 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
 		if (WARN_ON(ret))
 			break;
 
-		trans->block_rsv = rsv;
+		trans->block_rsv = &rsv;
 	}
 
 	/*
@@ -7768,7 +7766,7 @@ static int btrfs_truncate(struct btrfs_inode *inode, bool skip_writeback)
 		btrfs_btree_balance_dirty(fs_info);
 	}
 out:
-	btrfs_free_block_rsv(fs_info, rsv);
+	btrfs_block_rsv_release(fs_info, &rsv, (u64)-1, NULL);
 	/*
 	 * So if we truncate and then write and fsync we normally would just
 	 * write the extents that changed, which is a problem if we need to
-- 
2.47.1

[PATCH 3/3] btrfs: use on-stack variable for block reserve in btrfs_replace_file_extents()

[David Sterba]

We can avoid potential memory allocation failure in
btrfs_replace_file_extents() as the block reserve lifetime is limited to
the scope of the function. This requires +48 bytes on stack.

Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/file.c | 29 ++++++++++++-----------------
 1 file changed, 12 insertions(+), 17 deletions(-)

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 8ce6f45f45e0..2902de88dd1b 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2341,7 +2341,7 @@ int btrfs_replace_file_extents(struct btrfs_inode *inode,
 	u64 min_size = btrfs_calc_insert_metadata_size(fs_info, 1);
 	u64 ino_size = round_up(inode->vfs_inode.i_size, fs_info->sectorsize);
 	struct btrfs_trans_handle *trans = NULL;
-	struct btrfs_block_rsv *rsv;
+	struct btrfs_block_rsv rsv;
 	unsigned int rsv_count;
 	u64 cur_offset;
 	u64 len = end - start;
@@ -2350,13 +2350,9 @@ int btrfs_replace_file_extents(struct btrfs_inode *inode,
 	if (end <= start)
 		return -EINVAL;
 
-	rsv = btrfs_alloc_block_rsv(fs_info, BTRFS_BLOCK_RSV_TEMP);
-	if (!rsv) {
-		ret = -ENOMEM;
-		goto out;
-	}
-	rsv->size = btrfs_calc_insert_metadata_size(fs_info, 1);
-	rsv->failfast = true;
+	btrfs_init_metadata_block_rsv(fs_info, &rsv, BTRFS_BLOCK_RSV_TEMP);
+	rsv.size = btrfs_calc_insert_metadata_size(fs_info, 1);
+	rsv.failfast = true;
 
 	/*
 	 * 1 - update the inode
@@ -2373,14 +2369,14 @@ int btrfs_replace_file_extents(struct btrfs_inode *inode,
 	if (IS_ERR(trans)) {
 		ret = PTR_ERR(trans);
 		trans = NULL;
-		goto out_free;
+		goto out_release;
 	}
 
-	ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv, rsv,
+	ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv, &rsv,
 				      min_size, false);
 	if (WARN_ON(ret))
 		goto out_trans;
-	trans->block_rsv = rsv;
+	trans->block_rsv = &rsv;
 
 	cur_offset = start;
 	drop_args.path = path;
@@ -2496,10 +2492,10 @@ int btrfs_replace_file_extents(struct btrfs_inode *inode,
 		}
 
 		ret = btrfs_block_rsv_migrate(&fs_info->trans_block_rsv,
-					      rsv, min_size, false);
+					      &rsv, min_size, false);
 		if (WARN_ON(ret))
 			break;
-		trans->block_rsv = rsv;
+		trans->block_rsv = &rsv;
 
 		cur_offset = drop_args.drop_end;
 		len = end - cur_offset;
@@ -2576,16 +2572,15 @@ int btrfs_replace_file_extents(struct btrfs_inode *inode,
 
 out_trans:
 	if (!trans)
-		goto out_free;
+		goto out_release;
 
 	trans->block_rsv = &fs_info->trans_block_rsv;
 	if (ret)
 		btrfs_end_transaction(trans);
 	else
 		*trans_out = trans;
-out_free:
-	btrfs_free_block_rsv(fs_info, rsv);
-out:
+out_release:
+	btrfs_block_rsv_release(fs_info, &rsv, (u64)-1, NULL);
 	return ret;
 }
 
-- 
2.47.1