[v2,2/3] btrfs: qgroup: Try to flush qgroup space when we get -EDQUOT
diff mbox series

Message ID 20200703061902.33350-3-wqu@suse.com
State New
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Series
  • btrfs: qgroup: Fix the long existing regression of btrfs/153
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Commit Message

Qu Wenruo July 3, 2020, 6:19 a.m. UTC
[PROBLEM]
There are known problem related to how btrfs handles qgroup reserved
space.
One of the most obvious case is the the test case btrfs/153, which do
fallocate, then write into the preallocated range.

  btrfs/153 1s ... - output mismatch (see xfstests-dev/results//btrfs/153.out.bad)
      --- tests/btrfs/153.out     2019-10-22 15:18:14.068965341 +0800
      +++ xfstests-dev/results//btrfs/153.out.bad      2020-07-01 20:24:40.730000089 +0800
      @@ -1,2 +1,5 @@
       QA output created by 153
      +pwrite: Disk quota exceeded
      +/mnt/scratch/testfile2: Disk quota exceeded
      +/mnt/scratch/testfile2: Disk quota exceeded
       Silence is golden
      ...
      (Run 'diff -u xfstests-dev/tests/btrfs/153.out xfstests-dev/results//btrfs/153.out.bad'  to see the entire diff)

[CAUSE]
Since commit c6887cd11149 ("Btrfs: don't do nocow check unless we have to"),
we always reserve space no matter if it's COW or not.

Such behavior change is mostly for performance, and reverting it is not
a good idea anyway.

For preallcoated extent, we reserve qgroup data space for it already,
and since we also reserve data space for qgroup at buffered write time,
it needs twice the space for us to write into preallocated space.

This leads to the -EDQUOT in buffered write routine.

And we can't follow the same solution, unlike data/meta space check,
qgroup reserved space is shared between data/meta.
The EDQUOT can happen at the metadata reservation, so doing NODATACOW
check after qgroup reservation failure is not a solution.

[FIX]
To solve the problem, we don't return -EDQUOT directly, but every time
we got a -EDQUOT, we try to flush qgroup space by:
- Flush all inodes of the root
  NODATACOW writes will free the qgroup reserved at run_dealloc_range().
  However we don't have the infrastructure to only flush NODATACOW
  inodes, here we flush all inodes anyway.

- Wait ordered extents
  This would convert the preallocated metadata space into per-trans
  metadata, which can be freed in later transaction commit.

- Commit transaction
  This will free all per-trans metadata space.

Also we don't want to trigger flush too racy, so here we introduce a
per-root mutex to ensure if there is a running qgroup flushing, we wait
for it to end and don't start re-flush.

Fixes: c6887cd11149 ("Btrfs: don't do nocow check unless we have to")
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/ctree.h   |   1 +
 fs/btrfs/disk-io.c |   1 +
 fs/btrfs/qgroup.c  | 118 ++++++++++++++++++++++++++++++++++++++++-----
 3 files changed, 108 insertions(+), 12 deletions(-)

Comments

Josef Bacik July 6, 2020, 1:41 p.m. UTC | #1
On 7/3/20 2:19 AM, Qu Wenruo wrote:
> [PROBLEM]
> There are known problem related to how btrfs handles qgroup reserved
> space.
> One of the most obvious case is the the test case btrfs/153, which do
> fallocate, then write into the preallocated range.
> 
>    btrfs/153 1s ... - output mismatch (see xfstests-dev/results//btrfs/153.out.bad)
>        --- tests/btrfs/153.out     2019-10-22 15:18:14.068965341 +0800
>        +++ xfstests-dev/results//btrfs/153.out.bad      2020-07-01 20:24:40.730000089 +0800
>        @@ -1,2 +1,5 @@
>         QA output created by 153
>        +pwrite: Disk quota exceeded
>        +/mnt/scratch/testfile2: Disk quota exceeded
>        +/mnt/scratch/testfile2: Disk quota exceeded
>         Silence is golden
>        ...
>        (Run 'diff -u xfstests-dev/tests/btrfs/153.out xfstests-dev/results//btrfs/153.out.bad'  to see the entire diff)
> 
> [CAUSE]
> Since commit c6887cd11149 ("Btrfs: don't do nocow check unless we have to"),
> we always reserve space no matter if it's COW or not.
> 
> Such behavior change is mostly for performance, and reverting it is not
> a good idea anyway.
> 
> For preallcoated extent, we reserve qgroup data space for it already,
> and since we also reserve data space for qgroup at buffered write time,
> it needs twice the space for us to write into preallocated space.
> 
> This leads to the -EDQUOT in buffered write routine.
> 
> And we can't follow the same solution, unlike data/meta space check,
> qgroup reserved space is shared between data/meta.
> The EDQUOT can happen at the metadata reservation, so doing NODATACOW
> check after qgroup reservation failure is not a solution.
> 
> [FIX]
> To solve the problem, we don't return -EDQUOT directly, but every time
> we got a -EDQUOT, we try to flush qgroup space by:
> - Flush all inodes of the root
>    NODATACOW writes will free the qgroup reserved at run_dealloc_range().
>    However we don't have the infrastructure to only flush NODATACOW
>    inodes, here we flush all inodes anyway.
> 
> - Wait ordered extents
>    This would convert the preallocated metadata space into per-trans
>    metadata, which can be freed in later transaction commit.
> 
> - Commit transaction
>    This will free all per-trans metadata space.
> 
> Also we don't want to trigger flush too racy, so here we introduce a
> per-root mutex to ensure if there is a running qgroup flushing, we wait
> for it to end and don't start re-flush.
> 
> Fixes: c6887cd11149 ("Btrfs: don't do nocow check unless we have to")
> Signed-off-by: Qu Wenruo <wqu@suse.com>
> ---
>   fs/btrfs/ctree.h   |   1 +
>   fs/btrfs/disk-io.c |   1 +
>   fs/btrfs/qgroup.c  | 118 ++++++++++++++++++++++++++++++++++++++++-----
>   3 files changed, 108 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 4dd478b4fe3a..891f47c7891f 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -1162,6 +1162,7 @@ struct btrfs_root {
>   	spinlock_t qgroup_meta_rsv_lock;
>   	u64 qgroup_meta_rsv_pertrans;
>   	u64 qgroup_meta_rsv_prealloc;
> +	struct mutex qgroup_flushing_mutex;
>   
>   	/* Number of active swapfiles */
>   	atomic_t nr_swapfiles;
> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> index c27022f13150..0116e0b487c9 100644
> --- a/fs/btrfs/disk-io.c
> +++ b/fs/btrfs/disk-io.c
> @@ -1116,6 +1116,7 @@ static void __setup_root(struct btrfs_root *root, struct btrfs_fs_info *fs_info,
>   	mutex_init(&root->log_mutex);
>   	mutex_init(&root->ordered_extent_mutex);
>   	mutex_init(&root->delalloc_mutex);
> +	mutex_init(&root->qgroup_flushing_mutex);
>   	init_waitqueue_head(&root->log_writer_wait);
>   	init_waitqueue_head(&root->log_commit_wait[0]);
>   	init_waitqueue_head(&root->log_commit_wait[1]);
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index 398de1145d2b..bf9076bc33eb 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -3481,13 +3481,14 @@ static int qgroup_revert(struct btrfs_inode *inode,
>   		int clear_ret;
>   
>   		entry = rb_entry(n, struct ulist_node, rb_node);
> -		if (entry->val >= start + len)
> -			break;
> -		if (entry->val + entry->aux <= start)
> -			goto next;
>   		start = entry->val;
>   		end = entry->aux;
>   		len = end - start + 1;
> +
> +		if (start >= start + len)
> +			break;
> +		if (start + len <= start)
> +			goto next;

This is unrelated to the change at hand, put this in the 1st patch.

>   		/*
>   		 * Now the entry is in [start, start + len), revert the
>   		 * EXTENT_QGROUP_RESERVED bit.
> @@ -3512,17 +3513,62 @@ static int qgroup_revert(struct btrfs_inode *inode,
>   }
>   
>   /*
> - * Reserve qgroup space for range [start, start + len).
> + * Try to free some space for qgroup.
>    *
> - * This function will either reserve space from related qgroups or doing
> - * nothing if the range is already reserved.
> + * For qgroup, there are only 3 ways to free qgroup space:
> + * - Flush nodatacow write
> + *   Any nodatacow write will free its reserved data space at
> + *   run_delalloc_range().
> + *   In theory, we should only flush nodatacow inodes, but it's
> + *   not yet possible, so we need to flush the whole root.
>    *
> - * Return 0 for successful reserve
> - * Return <0 for error (including -EQUOT)
> + * - Wait for ordered extents
> + *   When ordered extents are finished, their reserved metadata
> + *   is finally converted to per_trans status, which can be freed
> + *   by later commit transaction.
>    *
> - * NOTE: this function may sleep for memory allocation.
> + * - Commit transaction
> + *   This would free the meta_per_trans space.
> + *   In theory this shouldn't provide much space, but any more qgroup space
> + *   is needed.
>    */
> -int btrfs_qgroup_reserve_data(struct btrfs_inode *inode,
> +static int try_flush_qgroup(struct btrfs_root *root)
> +{
> +	struct btrfs_trans_handle *trans;
> +	int ret;
> +
> +	if (!is_fstree(root->root_key.objectid))
> +		return 0;
> +

This will just retry the reservation again without having done anything.  Is it 
even possible to end up here with a !fs_tree?  If it is then maybe we should 
return -EDQUOT here so we don't retry the reservation again.

> +	/*
> +	 * We don't want to run flush again and again, so if there is a running
> +	 * one, we won't try to start a new flush, but exit directly.
> +	 */
> +	ret = mutex_trylock(&root->qgroup_flushing_mutex);
> +	if (!ret) {
> +		mutex_lock(&root->qgroup_flushing_mutex);
> +		mutex_unlock(&root->qgroup_flushing_mutex);
> +		return 0;
> +	}
> +
> +	ret = btrfs_start_delalloc_snapshot(root);
> +	if (ret < 0)
> +		goto unlock;
> +	btrfs_wait_ordered_extents(root, U64_MAX, 0, (u64)-1);
> +
> +	trans = btrfs_join_transaction(root);
> +	if (IS_ERR(trans)) {
> +		ret = PTR_ERR(trans);
> +		goto unlock;
> +	}
> +
> +	ret = btrfs_commit_transaction(trans);
> +unlock:
> +	mutex_unlock(&root->qgroup_flushing_mutex);
> +	return ret;
> +}

I still hate this but implementing tickets for quotas probably doesn't make 
sense right now.

<snip>

> +
> +	ret = qgroup_reserve_meta(root, num_bytes, type, enforce);
> +	if (!ret)
> +		return ret;
> +	if (ret < 0 && ret != -EDQUOT)
> +		return ret;

if (ret <= 0 && ret != -EDQUOT)
	return ret;

Thanks,

Josef
Qu Wenruo July 6, 2020, 1:46 p.m. UTC | #2
On 2020/7/6 下午9:41, Josef Bacik wrote:
> On 7/3/20 2:19 AM, Qu Wenruo wrote:
>> [PROBLEM]
>> There are known problem related to how btrfs handles qgroup reserved
>> space.
>> One of the most obvious case is the the test case btrfs/153, which do
>> fallocate, then write into the preallocated range.
>>
>>    btrfs/153 1s ... - output mismatch (see
>> xfstests-dev/results//btrfs/153.out.bad)
>>        --- tests/btrfs/153.out     2019-10-22 15:18:14.068965341 +0800
>>        +++ xfstests-dev/results//btrfs/153.out.bad      2020-07-01
>> 20:24:40.730000089 +0800
>>        @@ -1,2 +1,5 @@
>>         QA output created by 153
>>        +pwrite: Disk quota exceeded
>>        +/mnt/scratch/testfile2: Disk quota exceeded
>>        +/mnt/scratch/testfile2: Disk quota exceeded
>>         Silence is golden
>>        ...
>>        (Run 'diff -u xfstests-dev/tests/btrfs/153.out
>> xfstests-dev/results//btrfs/153.out.bad'  to see the entire diff)
>>
>> [CAUSE]
>> Since commit c6887cd11149 ("Btrfs: don't do nocow check unless we have
>> to"),
>> we always reserve space no matter if it's COW or not.
>>
>> Such behavior change is mostly for performance, and reverting it is not
>> a good idea anyway.
>>
>> For preallcoated extent, we reserve qgroup data space for it already,
>> and since we also reserve data space for qgroup at buffered write time,
>> it needs twice the space for us to write into preallocated space.
>>
>> This leads to the -EDQUOT in buffered write routine.
>>
>> And we can't follow the same solution, unlike data/meta space check,
>> qgroup reserved space is shared between data/meta.
>> The EDQUOT can happen at the metadata reservation, so doing NODATACOW
>> check after qgroup reservation failure is not a solution.
>>
>> [FIX]
>> To solve the problem, we don't return -EDQUOT directly, but every time
>> we got a -EDQUOT, we try to flush qgroup space by:
>> - Flush all inodes of the root
>>    NODATACOW writes will free the qgroup reserved at run_dealloc_range().
>>    However we don't have the infrastructure to only flush NODATACOW
>>    inodes, here we flush all inodes anyway.
>>
>> - Wait ordered extents
>>    This would convert the preallocated metadata space into per-trans
>>    metadata, which can be freed in later transaction commit.
>>
>> - Commit transaction
>>    This will free all per-trans metadata space.
>>
>> Also we don't want to trigger flush too racy, so here we introduce a
>> per-root mutex to ensure if there is a running qgroup flushing, we wait
>> for it to end and don't start re-flush.
>>
>> Fixes: c6887cd11149 ("Btrfs: don't do nocow check unless we have to")
>> Signed-off-by: Qu Wenruo <wqu@suse.com>
>> ---
>>   fs/btrfs/ctree.h   |   1 +
>>   fs/btrfs/disk-io.c |   1 +
>>   fs/btrfs/qgroup.c  | 118 ++++++++++++++++++++++++++++++++++++++++-----
>>   3 files changed, 108 insertions(+), 12 deletions(-)
>>
>> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
>> index 4dd478b4fe3a..891f47c7891f 100644
>> --- a/fs/btrfs/ctree.h
>> +++ b/fs/btrfs/ctree.h
>> @@ -1162,6 +1162,7 @@ struct btrfs_root {
>>       spinlock_t qgroup_meta_rsv_lock;
>>       u64 qgroup_meta_rsv_pertrans;
>>       u64 qgroup_meta_rsv_prealloc;
>> +    struct mutex qgroup_flushing_mutex;
>>         /* Number of active swapfiles */
>>       atomic_t nr_swapfiles;
>> diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
>> index c27022f13150..0116e0b487c9 100644
>> --- a/fs/btrfs/disk-io.c
>> +++ b/fs/btrfs/disk-io.c
>> @@ -1116,6 +1116,7 @@ static void __setup_root(struct btrfs_root
>> *root, struct btrfs_fs_info *fs_info,
>>       mutex_init(&root->log_mutex);
>>       mutex_init(&root->ordered_extent_mutex);
>>       mutex_init(&root->delalloc_mutex);
>> +    mutex_init(&root->qgroup_flushing_mutex);
>>       init_waitqueue_head(&root->log_writer_wait);
>>       init_waitqueue_head(&root->log_commit_wait[0]);
>>       init_waitqueue_head(&root->log_commit_wait[1]);
>> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
>> index 398de1145d2b..bf9076bc33eb 100644
>> --- a/fs/btrfs/qgroup.c
>> +++ b/fs/btrfs/qgroup.c
>> @@ -3481,13 +3481,14 @@ static int qgroup_revert(struct btrfs_inode
>> *inode,
>>           int clear_ret;
>>             entry = rb_entry(n, struct ulist_node, rb_node);
>> -        if (entry->val >= start + len)
>> -            break;
>> -        if (entry->val + entry->aux <= start)
>> -            goto next;
>>           start = entry->val;
>>           end = entry->aux;
>>           len = end - start + 1;
>> +
>> +        if (start >= start + len)
>> +            break;
>> +        if (start + len <= start)
>> +            goto next;
> 
> This is unrelated to the change at hand, put this in the 1st patch.
> 
>>           /*
>>            * Now the entry is in [start, start + len), revert the
>>            * EXTENT_QGROUP_RESERVED bit.
>> @@ -3512,17 +3513,62 @@ static int qgroup_revert(struct btrfs_inode
>> *inode,
>>   }
>>     /*
>> - * Reserve qgroup space for range [start, start + len).
>> + * Try to free some space for qgroup.
>>    *
>> - * This function will either reserve space from related qgroups or doing
>> - * nothing if the range is already reserved.
>> + * For qgroup, there are only 3 ways to free qgroup space:
>> + * - Flush nodatacow write
>> + *   Any nodatacow write will free its reserved data space at
>> + *   run_delalloc_range().
>> + *   In theory, we should only flush nodatacow inodes, but it's
>> + *   not yet possible, so we need to flush the whole root.
>>    *
>> - * Return 0 for successful reserve
>> - * Return <0 for error (including -EQUOT)
>> + * - Wait for ordered extents
>> + *   When ordered extents are finished, their reserved metadata
>> + *   is finally converted to per_trans status, which can be freed
>> + *   by later commit transaction.
>>    *
>> - * NOTE: this function may sleep for memory allocation.
>> + * - Commit transaction
>> + *   This would free the meta_per_trans space.
>> + *   In theory this shouldn't provide much space, but any more qgroup
>> space
>> + *   is needed.
>>    */
>> -int btrfs_qgroup_reserve_data(struct btrfs_inode *inode,
>> +static int try_flush_qgroup(struct btrfs_root *root)
>> +{
>> +    struct btrfs_trans_handle *trans;
>> +    int ret;
>> +
>> +    if (!is_fstree(root->root_key.objectid))
>> +        return 0;
>> +
> 
> This will just retry the reservation again without having done
> anything.  Is it even possible to end up here with a !fs_tree?

You're right, it's impossible.

The existing btrfs_qgroup_reserve_data() has extra check for root
objectid, and just return 0 for non fs trees.
So it's impossible to hit the !is_fstree() branch.

>  If it is
> then maybe we should return -EDQUOT here so we don't retry the
> reservation again.
> 
>> +    /*
>> +     * We don't want to run flush again and again, so if there is a
>> running
>> +     * one, we won't try to start a new flush, but exit directly.
>> +     */
>> +    ret = mutex_trylock(&root->qgroup_flushing_mutex);
>> +    if (!ret) {
>> +        mutex_lock(&root->qgroup_flushing_mutex);
>> +        mutex_unlock(&root->qgroup_flushing_mutex);
>> +        return 0;
>> +    }
>> +
>> +    ret = btrfs_start_delalloc_snapshot(root);
>> +    if (ret < 0)
>> +        goto unlock;
>> +    btrfs_wait_ordered_extents(root, U64_MAX, 0, (u64)-1);
>> +
>> +    trans = btrfs_join_transaction(root);
>> +    if (IS_ERR(trans)) {
>> +        ret = PTR_ERR(trans);
>> +        goto unlock;
>> +    }
>> +
>> +    ret = btrfs_commit_transaction(trans);
>> +unlock:
>> +    mutex_unlock(&root->qgroup_flushing_mutex);
>> +    return ret;
>> +}
> 
> I still hate this but implementing tickets for quotas probably doesn't
> make sense right now.

Yep. But I'm pretty open to integrating this into the tickets system.

Thanks,
Qu
> 
> <snip>
> 
>> +
>> +    ret = qgroup_reserve_meta(root, num_bytes, type, enforce);
>> +    if (!ret)
>> +        return ret;
>> +    if (ret < 0 && ret != -EDQUOT)
>> +        return ret;
> 
> if (ret <= 0 && ret != -EDQUOT)
>     return ret;
> 
> Thanks,
> 
> Josef
>

Patch
diff mbox series

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 4dd478b4fe3a..891f47c7891f 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1162,6 +1162,7 @@  struct btrfs_root {
 	spinlock_t qgroup_meta_rsv_lock;
 	u64 qgroup_meta_rsv_pertrans;
 	u64 qgroup_meta_rsv_prealloc;
+	struct mutex qgroup_flushing_mutex;
 
 	/* Number of active swapfiles */
 	atomic_t nr_swapfiles;
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index c27022f13150..0116e0b487c9 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1116,6 +1116,7 @@  static void __setup_root(struct btrfs_root *root, struct btrfs_fs_info *fs_info,
 	mutex_init(&root->log_mutex);
 	mutex_init(&root->ordered_extent_mutex);
 	mutex_init(&root->delalloc_mutex);
+	mutex_init(&root->qgroup_flushing_mutex);
 	init_waitqueue_head(&root->log_writer_wait);
 	init_waitqueue_head(&root->log_commit_wait[0]);
 	init_waitqueue_head(&root->log_commit_wait[1]);
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index 398de1145d2b..bf9076bc33eb 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -3481,13 +3481,14 @@  static int qgroup_revert(struct btrfs_inode *inode,
 		int clear_ret;
 
 		entry = rb_entry(n, struct ulist_node, rb_node);
-		if (entry->val >= start + len)
-			break;
-		if (entry->val + entry->aux <= start)
-			goto next;
 		start = entry->val;
 		end = entry->aux;
 		len = end - start + 1;
+
+		if (start >= start + len)
+			break;
+		if (start + len <= start)
+			goto next;
 		/*
 		 * Now the entry is in [start, start + len), revert the
 		 * EXTENT_QGROUP_RESERVED bit.
@@ -3512,17 +3513,62 @@  static int qgroup_revert(struct btrfs_inode *inode,
 }
 
 /*
- * Reserve qgroup space for range [start, start + len).
+ * Try to free some space for qgroup.
  *
- * This function will either reserve space from related qgroups or doing
- * nothing if the range is already reserved.
+ * For qgroup, there are only 3 ways to free qgroup space:
+ * - Flush nodatacow write
+ *   Any nodatacow write will free its reserved data space at
+ *   run_delalloc_range().
+ *   In theory, we should only flush nodatacow inodes, but it's
+ *   not yet possible, so we need to flush the whole root.
  *
- * Return 0 for successful reserve
- * Return <0 for error (including -EQUOT)
+ * - Wait for ordered extents
+ *   When ordered extents are finished, their reserved metadata
+ *   is finally converted to per_trans status, which can be freed
+ *   by later commit transaction.
  *
- * NOTE: this function may sleep for memory allocation.
+ * - Commit transaction
+ *   This would free the meta_per_trans space.
+ *   In theory this shouldn't provide much space, but any more qgroup space
+ *   is needed.
  */
-int btrfs_qgroup_reserve_data(struct btrfs_inode *inode,
+static int try_flush_qgroup(struct btrfs_root *root)
+{
+	struct btrfs_trans_handle *trans;
+	int ret;
+
+	if (!is_fstree(root->root_key.objectid))
+		return 0;
+
+	/*
+	 * We don't want to run flush again and again, so if there is a running
+	 * one, we won't try to start a new flush, but exit directly.
+	 */
+	ret = mutex_trylock(&root->qgroup_flushing_mutex);
+	if (!ret) {
+		mutex_lock(&root->qgroup_flushing_mutex);
+		mutex_unlock(&root->qgroup_flushing_mutex);
+		return 0;
+	}
+
+	ret = btrfs_start_delalloc_snapshot(root);
+	if (ret < 0)
+		goto unlock;
+	btrfs_wait_ordered_extents(root, U64_MAX, 0, (u64)-1);
+
+	trans = btrfs_join_transaction(root);
+	if (IS_ERR(trans)) {
+		ret = PTR_ERR(trans);
+		goto unlock;
+	}
+
+	ret = btrfs_commit_transaction(trans);
+unlock:
+	mutex_unlock(&root->qgroup_flushing_mutex);
+	return ret;
+}
+
+static int qgroup_reserve_data(struct btrfs_inode *inode,
 			struct extent_changeset **reserved_ret, u64 start,
 			u64 len)
 {
@@ -3575,6 +3621,37 @@  int btrfs_qgroup_reserve_data(struct btrfs_inode *inode,
 	return ret;
 }
 
+/*
+ * Reserve qgroup space for range [start, start + len).
+ *
+ * This function will either reserve space from related qgroups or doing
+ * nothing if the range is already reserved.
+ *
+ * Return 0 for successful reserve
+ * Return <0 for error (including -EQUOT)
+ *
+ * NOTE: This function may sleep for memory allocation, dirty page flushing and
+ *	 commit transaction. So caller should not hold any dirty page locked.
+ */
+int btrfs_qgroup_reserve_data(struct btrfs_inode *inode,
+			struct extent_changeset **reserved_ret, u64 start,
+			u64 len)
+{
+	int ret;
+
+	ret = qgroup_reserve_data(inode, reserved_ret, start, len);
+	if (!ret)
+		return ret;
+
+	if (ret < 0 && ret != -EDQUOT)
+		return ret;
+
+	ret = try_flush_qgroup(inode->root);
+	if (ret < 0)
+		return ret;
+	return qgroup_reserve_data(inode, reserved_ret, start, len);
+}
+
 /* Free ranges specified by @reserved, normally in error path */
 static int qgroup_free_reserved_data(struct btrfs_inode *inode,
 			struct extent_changeset *reserved, u64 start, u64 len)
@@ -3743,7 +3820,7 @@  static int sub_root_meta_rsv(struct btrfs_root *root, int num_bytes,
 	return num_bytes;
 }
 
-int __btrfs_qgroup_reserve_meta(struct btrfs_root *root, int num_bytes,
+static int qgroup_reserve_meta(struct btrfs_root *root, int num_bytes,
 				enum btrfs_qgroup_rsv_type type, bool enforce)
 {
 	struct btrfs_fs_info *fs_info = root->fs_info;
@@ -3770,6 +3847,23 @@  int __btrfs_qgroup_reserve_meta(struct btrfs_root *root, int num_bytes,
 	return ret;
 }
 
+int __btrfs_qgroup_reserve_meta(struct btrfs_root *root, int num_bytes,
+				enum btrfs_qgroup_rsv_type type, bool enforce)
+{
+	int ret;
+
+	ret = qgroup_reserve_meta(root, num_bytes, type, enforce);
+	if (!ret)
+		return ret;
+	if (ret < 0 && ret != -EDQUOT)
+		return ret;
+
+	ret = try_flush_qgroup(root);
+	if (ret < 0)
+		return ret;
+	return qgroup_reserve_meta(root, num_bytes, type, enforce);
+}
+
 void btrfs_qgroup_free_meta_all_pertrans(struct btrfs_root *root)
 {
 	struct btrfs_fs_info *fs_info = root->fs_info;