btrfs: qgroup: Use independent and accurate per inode qgroup rsv

Unlike reservation calculation used in inode rsv for metadata, qgroup
doesn't really need to care about things like csum size or extent usage
for the whole tree COW.

Qgroups care more about net change of the extent usage.
That's to say, if we're going to insert one file extent, it will mostly
find its place in COWed tree block, leaving no change in extent usage.
Or causing a leaf split, resulting in one new net extent and increasing
qgroup number by nodesize.
Or in an even more rare case, increase the tree level, increasing qgroup
number by 2 * nodesize.

So here instead of using the complicated calculation for extent
allocator, which cares more about accuracy and no error, qgroup doesn't
need that over-estimated reservation.

This patch will maintain 2 new members in btrfs_block_rsv structure for
qgroup, using much smaller calculation for qgroup rsv, reducing false
EDQUOT.

Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>

fs/btrfs/ctree.h

@@ -459,6 +459,25 @@ struct btrfs_block_rsv {
 	unsigned short full;
 	unsigned short type;
 	unsigned short failfast;
+
+	/*
+	 * Qgroup equivalent for @size @reserved
+	 *
+	 * Unlike normal @size/@reserved for inode rsv, qgroup doesn't care
+	 * about things like csum size nor how many tree blocks it will need to
+	 * reserve.
+	 *
+	 * Qgroup cares more about net change of the extent usage.
+	 *
+	 * So for one newly inserted file extent, in worst case it will cause
+	 * leaf split and level increase, nodesize for each file extent is
+	 * already too much.
+	 *
+	 * In short, qgroup_size/reserved is the upper limit of possible needed
+	 * qgroup metadata reservation.
+	 */
+	u64 qgroup_rsv_size;
+	u64 qgroup_rsv_reserved;
 };
 
 /*

fs/btrfs/extent-tree.c

@@ -5560,14 +5560,18 @@ again:
 
 static u64 block_rsv_release_bytes(struct btrfs_fs_info *fs_info,
 				    struct btrfs_block_rsv *block_rsv,
-				    struct btrfs_block_rsv *dest, u64 num_bytes)
+				    struct btrfs_block_rsv *dest, u64 num_bytes,
+				    u64 *qgroup_to_release_ret)
 {
 	struct btrfs_space_info *space_info = block_rsv->space_info;
+	u64 qgroup_to_release = 0;
 	u64 ret;
 
 	spin_lock(&block_rsv->lock);
-	if (num_bytes == (u64)-1)
+	if (num_bytes == (u64)-1) {
 		num_bytes = block_rsv->size;
+		qgroup_to_release = block_rsv->qgroup_rsv_size;
+	}
 	block_rsv->size -= num_bytes;
 	if (block_rsv->reserved >= block_rsv->size) {
 		num_bytes = block_rsv->reserved - block_rsv->size;
@@ -5576,6 +5580,13 @@ static u64 block_rsv_release_bytes(struct btrfs_fs_info *fs_info,
 	} else {
 		num_bytes = 0;
 	}
+	if (block_rsv->qgroup_rsv_reserved >= block_rsv->qgroup_rsv_size) {
+		qgroup_to_release = block_rsv->qgroup_rsv_reserved -
+				    block_rsv->qgroup_rsv_size;
+		block_rsv->qgroup_rsv_reserved = block_rsv->qgroup_rsv_size;
+	} else {
+		qgroup_to_release = 0;
+	}
 	spin_unlock(&block_rsv->lock);
 
 	ret = num_bytes;
@@ -5598,6 +5609,8 @@ static u64 block_rsv_release_bytes(struct btrfs_fs_info *fs_info,
 			space_info_add_old_bytes(fs_info, space_info,
 						 num_bytes);
 	}
+	if (qgroup_to_release_ret)
+		*qgroup_to_release_ret = qgroup_to_release;
 	return ret;
 }
 
@@ -5739,17 +5752,21 @@ static int btrfs_inode_rsv_refill(struct btrfs_inode *inode,
 	struct btrfs_root *root = inode->root;
 	struct btrfs_block_rsv *block_rsv = &inode->block_rsv;
 	u64 num_bytes = 0;
+	u64 qgroup_num_bytes = 0;
 	int ret = -ENOSPC;
 
 	spin_lock(&block_rsv->lock);
 	if (block_rsv->reserved < block_rsv->size)
 		num_bytes = block_rsv->size - block_rsv->reserved;
+	if (block_rsv->qgroup_rsv_reserved < block_rsv->qgroup_rsv_size)
+		qgroup_num_bytes = block_rsv->qgroup_rsv_size -
+				   block_rsv->qgroup_rsv_reserved;
 	spin_unlock(&block_rsv->lock);
 
 	if (num_bytes == 0)
 		return 0;
 
-	ret = btrfs_qgroup_reserve_meta_prealloc(root, num_bytes, true);
+	ret = btrfs_qgroup_reserve_meta_prealloc(root, qgroup_num_bytes, true);
 	if (ret)
 		return ret;
 	ret = reserve_metadata_bytes(root, block_rsv, num_bytes, flush);
@@ -5757,7 +5774,13 @@ static int btrfs_inode_rsv_refill(struct btrfs_inode *inode,
 		block_rsv_add_bytes(block_rsv, num_bytes, 0);
 		trace_btrfs_space_reservation(root->fs_info, "delalloc",
 					      btrfs_ino(inode), num_bytes, 1);
-	}
+
+		/* Don't forget to increase qgroup_rsv_reserved */
+		spin_lock(&block_rsv->lock);
+		block_rsv->qgroup_rsv_reserved += qgroup_num_bytes;
+		spin_unlock(&block_rsv->lock);
+	} else
+		btrfs_qgroup_free_meta_prealloc(root, qgroup_num_bytes);
 	return ret;
 }
 
@@ -5778,20 +5801,23 @@ static void btrfs_inode_rsv_release(struct btrfs_inode *inode, bool qgroup_free)
 	struct btrfs_block_rsv *global_rsv = &fs_info->global_block_rsv;
 	struct btrfs_block_rsv *block_rsv = &inode->block_rsv;
 	u64 released = 0;
+	u64 qgroup_to_release = 0;
 
 	/*
 	 * Since we statically set the block_rsv->size we just want to say we
 	 * are releasing 0 bytes, and then we'll just get the reservation over
 	 * the size free'd.
 	 */
-	released = block_rsv_release_bytes(fs_info, block_rsv, global_rsv, 0);
+	released = block_rsv_release_bytes(fs_info, block_rsv, global_rsv, 0,
+					   &qgroup_to_release);
 	if (released > 0)
 		trace_btrfs_space_reservation(fs_info, "delalloc",
 					      btrfs_ino(inode), released, 0);
 	if (qgroup_free)
-		btrfs_qgroup_free_meta_prealloc(inode->root, released);
+		btrfs_qgroup_free_meta_prealloc(inode->root, qgroup_to_release);
 	else
-		btrfs_qgroup_convert_reserved_meta(inode->root, released);
+		btrfs_qgroup_convert_reserved_meta(inode->root,
+						   qgroup_to_release);
 }
 
 void btrfs_block_rsv_release(struct btrfs_fs_info *fs_info,
@@ -5803,7 +5829,7 @@ void btrfs_block_rsv_release(struct btrfs_fs_info *fs_info,
 	if (global_rsv == block_rsv ||
 	    block_rsv->space_info != global_rsv->space_info)
 		global_rsv = NULL;
-	block_rsv_release_bytes(fs_info, block_rsv, global_rsv, num_bytes);
+	block_rsv_release_bytes(fs_info, block_rsv, global_rsv, num_bytes, NULL);
 }
 
 static void update_global_block_rsv(struct btrfs_fs_info *fs_info)
@@ -5883,7 +5909,7 @@ static void init_global_block_rsv(struct btrfs_fs_info *fs_info)
 static void release_global_block_rsv(struct btrfs_fs_info *fs_info)
 {
 	block_rsv_release_bytes(fs_info, &fs_info->global_block_rsv, NULL,
-				(u64)-1);
+				(u64)-1, NULL);
 	WARN_ON(fs_info->trans_block_rsv.size > 0);
 	WARN_ON(fs_info->trans_block_rsv.reserved > 0);
 	WARN_ON(fs_info->chunk_block_rsv.size > 0);
@@ -5907,7 +5933,7 @@ void btrfs_trans_release_chunk_metadata(struct btrfs_trans_handle *trans)
 	WARN_ON_ONCE(!list_empty(&trans->new_bgs));
 
 	block_rsv_release_bytes(fs_info, &fs_info->chunk_block_rsv, NULL,
-				trans->chunk_bytes_reserved);
+				trans->chunk_bytes_reserved, NULL);
 	trans->chunk_bytes_reserved = 0;
 }
 
@@ -6012,6 +6038,7 @@ static void btrfs_calculate_inode_block_rsv_size(struct btrfs_fs_info *fs_info,
 {
 	struct btrfs_block_rsv *block_rsv = &inode->block_rsv;
 	u64 reserve_size = 0;
+	u64 qgroup_rsv_size = 0;
 	u64 csum_leaves;
 	unsigned outstanding_extents;
 
@@ -6024,9 +6051,17 @@ static void btrfs_calculate_inode_block_rsv_size(struct btrfs_fs_info *fs_info,
 						 inode->csum_bytes);
 	reserve_size += btrfs_calc_trans_metadata_size(fs_info,
 						       csum_leaves);
+	/*
+	 * For qgroup rsv, the calculation is very simple:
+	 * account one nodesize for each outstanding extent
+	 *
+	 * This is overestimating in most cases.
+	 */
+	qgroup_rsv_size = outstanding_extents * fs_info->nodesize;
 
 	spin_lock(&block_rsv->lock);
 	block_rsv->size = reserve_size;
+	block_rsv->qgroup_rsv_size = qgroup_rsv_size;
 	spin_unlock(&block_rsv->lock);
 }
 
@@ -8405,7 +8440,7 @@ static void unuse_block_rsv(struct btrfs_fs_info *fs_info,
 			    struct btrfs_block_rsv *block_rsv, u32 blocksize)
 {
 	block_rsv_add_bytes(block_rsv, blocksize, 0);
-	block_rsv_release_bytes(fs_info, block_rsv, NULL, 0);
+	block_rsv_release_bytes(fs_info, block_rsv, NULL, 0, NULL);
 }
 
 /*