Commit fb235dc0 authored by Qu Wenruo's avatar Qu Wenruo Committed by David Sterba
Browse files

btrfs: qgroup: Move half of the qgroup accounting time out of commit trans 



Just as Filipe pointed out, the most time consuming parts of qgroup are
btrfs_qgroup_account_extents() and
btrfs_qgroup_prepare_account_extents().
Which both call btrfs_find_all_roots() to get old_roots and new_roots
ulist.

What makes things worse is, we're calling that expensive
btrfs_find_all_roots() at transaction committing time with
TRANS_STATE_COMMIT_DOING, which will blocks all incoming transaction.

Such behavior is necessary for @new_roots search as current
btrfs_find_all_roots() can't do it correctly so we do call it just
before switch commit roots.

However for @old_roots search, it's not necessary as such search is
based on commit_root, so it will always be correct and we can move it
out of transaction committing.

This patch moves the @old_roots search part out of
commit_transaction(), so in theory we can half the time qgroup time
consumption at commit_transaction().

But please note that, this won't speedup qgroup overall, the total time
consumption is still the same, just reduce the performance stall.

Cc: Filipe Manana <fdmanana@suse.com>
Signed-off-by: default avatarQu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: default avatarFilipe Manana <fdmanana@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 15b34517

fs/btrfs/delayed-ref.c

+16 −4
Original line number Diff line number Diff line
@@ -550,13 +550,14 @@ add_delayed_ref_head(struct btrfs_fs_info *fs_info, 
		     struct btrfs_delayed_ref_node *ref,

		     struct btrfs_qgroup_extent_record *qrecord,

		     u64 bytenr, u64 num_bytes, u64 ref_root, u64 reserved,

		     int action, int is_data)

		     int action, int is_data, int *qrecord_inserted_ret)

{

	struct btrfs_delayed_ref_head *existing;

	struct btrfs_delayed_ref_head *head_ref = NULL;

	struct btrfs_delayed_ref_root *delayed_refs;

	int count_mod = 1;

	int must_insert_reserved = 0;

	int qrecord_inserted = 0;



	/* If reserved is provided, it must be a data extent. */

	BUG_ON(!is_data && reserved);
@@ -623,6 +624,8 @@ add_delayed_ref_head(struct btrfs_fs_info *fs_info, 
		if(btrfs_qgroup_trace_extent_nolock(fs_info,

					delayed_refs, qrecord))

			kfree(qrecord);

		else

			qrecord_inserted = 1;

	}



	spin_lock_init(&head_ref->lock);
@@ -650,6 +653,8 @@ add_delayed_ref_head(struct btrfs_fs_info *fs_info, 
		atomic_inc(&delayed_refs->num_entries);

		trans->delayed_ref_updates++;

	}

	if (qrecord_inserted_ret)

		*qrecord_inserted_ret = qrecord_inserted;

	return head_ref;

}
@@ -779,6 +784,7 @@ int btrfs_add_delayed_tree_ref(struct btrfs_fs_info *fs_info, 
	struct btrfs_delayed_ref_head *head_ref;

	struct btrfs_delayed_ref_root *delayed_refs;

	struct btrfs_qgroup_extent_record *record = NULL;

	int qrecord_inserted;



	BUG_ON(extent_op && extent_op->is_data);

	ref = kmem_cache_alloc(btrfs_delayed_tree_ref_cachep, GFP_NOFS);
@@ -806,12 +812,15 @@ int btrfs_add_delayed_tree_ref(struct btrfs_fs_info *fs_info, 
	 * the spin lock

	 */

	head_ref = add_delayed_ref_head(fs_info, trans, &head_ref->node, record,

					bytenr, num_bytes, 0, 0, action, 0);

					bytenr, num_bytes, 0, 0, action, 0,

					&qrecord_inserted);



	add_delayed_tree_ref(fs_info, trans, head_ref, &ref->node, bytenr,

			     num_bytes, parent, ref_root, level, action);

	spin_unlock(&delayed_refs->lock);



	if (qrecord_inserted)

		return btrfs_qgroup_trace_extent_post(fs_info, record);

	return 0;



free_head_ref:
@@ -835,6 +844,7 @@ int btrfs_add_delayed_data_ref(struct btrfs_fs_info *fs_info, 
	struct btrfs_delayed_ref_head *head_ref;

	struct btrfs_delayed_ref_root *delayed_refs;

	struct btrfs_qgroup_extent_record *record = NULL;

	int qrecord_inserted;



	ref = kmem_cache_alloc(btrfs_delayed_data_ref_cachep, GFP_NOFS);

	if (!ref)
@@ -868,13 +878,15 @@ int btrfs_add_delayed_data_ref(struct btrfs_fs_info *fs_info, 
	 */

	head_ref = add_delayed_ref_head(fs_info, trans, &head_ref->node, record,

					bytenr, num_bytes, ref_root, reserved,

					action, 1);

					action, 1, &qrecord_inserted);



	add_delayed_data_ref(fs_info, trans, head_ref, &ref->node, bytenr,

				   num_bytes, parent, ref_root, owner, offset,

				   action);

	spin_unlock(&delayed_refs->lock);



	if (qrecord_inserted)

		return btrfs_qgroup_trace_extent_post(fs_info, record);

	return 0;

}
@@ -897,7 +909,7 @@ int btrfs_add_delayed_extent_op(struct btrfs_fs_info *fs_info, 


	add_delayed_ref_head(fs_info, trans, &head_ref->node, NULL, bytenr,

			     num_bytes, 0, 0, BTRFS_UPDATE_DELAYED_HEAD,

			     extent_op->is_data);

			     extent_op->is_data, NULL);



	spin_unlock(&delayed_refs->lock);

	return 0;

fs/btrfs/qgroup.c

+29 −4
Original line number Diff line number Diff line
@@ -1464,8 +1464,9 @@ int btrfs_qgroup_prepare_account_extents(struct btrfs_trans_handle *trans, 
	while (node) {

		record = rb_entry(node, struct btrfs_qgroup_extent_record,

				  node);

		ret = btrfs_find_all_roots(NULL, fs_info, record->bytenr, 0,

					   &record->old_roots);

		if (WARN_ON(!record->old_roots))

			ret = btrfs_find_all_roots(NULL, fs_info,

					record->bytenr, 0, &record->old_roots);

		if (ret < 0)

			break;

		if (qgroup_to_skip)
@@ -1504,6 +1505,28 @@ int btrfs_qgroup_trace_extent_nolock(struct btrfs_fs_info *fs_info, 
	return 0;

}



int btrfs_qgroup_trace_extent_post(struct btrfs_fs_info *fs_info,

				   struct btrfs_qgroup_extent_record *qrecord)

{

	struct ulist *old_root;

	u64 bytenr = qrecord->bytenr;

	int ret;



	ret = btrfs_find_all_roots(NULL, fs_info, bytenr, 0, &old_root);

	if (ret < 0)

		return ret;



	/*

	 * Here we don't need to get the lock of

	 * trans->transaction->delayed_refs, since inserted qrecord won't

	 * be deleted, only qrecord->node may be modified (new qrecord insert)

	 *

	 * So modifying qrecord->old_roots is safe here

	 */

	qrecord->old_roots = old_root;

	return 0;

}



int btrfs_qgroup_trace_extent(struct btrfs_trans_handle *trans,

		struct btrfs_fs_info *fs_info, u64 bytenr, u64 num_bytes,

		gfp_t gfp_flag)
@@ -1529,10 +1552,12 @@ int btrfs_qgroup_trace_extent(struct btrfs_trans_handle *trans, 
	spin_lock(&delayed_refs->lock);

	ret = btrfs_qgroup_trace_extent_nolock(fs_info, delayed_refs, record);

	spin_unlock(&delayed_refs->lock);

	if (ret > 0)

	if (ret > 0) {

		kfree(record);

		return 0;

	}

	return btrfs_qgroup_trace_extent_post(fs_info, record);

}



int btrfs_qgroup_trace_leaf_items(struct btrfs_trans_handle *trans,

				  struct btrfs_fs_info *fs_info,

fs/btrfs/qgroup.h

+30 −3
Original line number Diff line number Diff line
@@ -94,9 +94,10 @@ int btrfs_qgroup_prepare_account_extents(struct btrfs_trans_handle *trans, 
					 struct btrfs_fs_info *fs_info);

/*

 * Inform qgroup to trace one dirty extent, its info is recorded in @record.

 * So qgroup can account it at commit trans time.

 * So qgroup can account it at transaction committing time.

 *

 * No lock version, caller must acquire delayed ref lock and allocate memory.

 * No lock version, caller must acquire delayed ref lock and allocated memory,

 * then call btrfs_qgroup_trace_extent_post() after exiting lock context.

 *

 * Return 0 for success insert

 * Return >0 for existing record, caller can free @record safely.
@@ -107,12 +108,38 @@ int btrfs_qgroup_trace_extent_nolock( 
		struct btrfs_delayed_ref_root *delayed_refs,

		struct btrfs_qgroup_extent_record *record);



/*

 * Post handler after qgroup_trace_extent_nolock().

 *

 * NOTE: Current qgroup does the expensive backref walk at transaction

 * committing time with TRANS_STATE_COMMIT_DOING, this blocks incoming

 * new transaction.

 * This is designed to allow btrfs_find_all_roots() to get correct new_roots

 * result.

 *

 * However for old_roots there is no need to do backref walk at that time,

 * since we search commit roots to walk backref and result will always be

 * correct.

 *

 * Due to the nature of no lock version, we can't do backref there.

 * So we must call btrfs_qgroup_trace_extent_post() after exiting

 * spinlock context.

 *

 * TODO: If we can fix and prove btrfs_find_all_roots() can get correct result

 * using current root, then we can move all expensive backref walk out of

 * transaction committing, but not now as qgroup accounting will be wrong again.

 */

int btrfs_qgroup_trace_extent_post(struct btrfs_fs_info *fs_info,

				   struct btrfs_qgroup_extent_record *qrecord);



/*

 * Inform qgroup to trace one dirty extent, specified by @bytenr and

 * @num_bytes.

 * So qgroup can account it at commit trans time.

 *

 * Better encapsulated version.

 * Better encapsulated version, with memory allocation and backref walk for

 * commit roots.

 * So this can sleep.

 *

 * Return 0 if the operation is done.

 * Return <0 for error, like memory allocation failure or invalid parameter

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