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Commit 823ae5b8 authored by Qu Wenruo's avatar Qu Wenruo Committed by Chris Mason
Browse files

btrfs: qgroup: Add function qgroup_update_counters(). 



Add function qgroup_update_counters(), which will update related
qgroups' rfer/excl according to old/new_roots.

This is one of the two core functions for the new qgroup implement.

This is based on btrfs_adjust_coutners() but with clearer logic and
comment.

Signed-off-by: default avatarQu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: default avatarChris Mason <clm@fb.com>
parent d810ef2b

fs/btrfs/qgroup.c

+120 −0
Original line number Diff line number Diff line
@@ -1864,6 +1864,126 @@ static int qgroup_update_refcnt(struct btrfs_fs_info *fs_info, 
	return 0;

}



/*

 * Update qgroup rfer/excl counters.

 * Rfer update is easy, codes can explain themselves.

 * Excl update is tricky, the update is split into 2 part.

 * Part 1: Possible exclusive <-> sharing detect:

 *	|	A	|	!A	|

 *  -------------------------------------

 *  B	|	*	|	-	|

 *  -------------------------------------

 *  !B	|	+	|	**	|

 *  -------------------------------------

 *

 * Conditions:

 * A:	cur_old_roots < nr_old_roots	(not exclusive before)

 * !A:	cur_old_roots == nr_old_roots	(possible exclusive before)

 * B:	cur_new_roots < nr_new_roots	(not exclusive now)

 * !B:	cur_new_roots == nr_new_roots	(possible exclsuive now)

 *

 * Results:

 * +: Possible sharing -> exclusive	-: Possible exclusive -> sharing

 * *: Definitely not changed.		**: Possible unchanged.

 *

 * For !A and !B condition, the exception is cur_old/new_roots == 0 case.

 *

 * To make the logic clear, we first use condition A and B to split

 * combination into 4 results.

 *

 * Then, for result "+" and "-", check old/new_roots == 0 case, as in them

 * only on variant maybe 0.

 *

 * Lastly, check result **, since there are 2 variants maybe 0, split them

 * again(2x2).

 * But this time we don't need to consider other things, the codes and logic

 * is easy to understand now.

 */

static int qgroup_update_counters(struct btrfs_fs_info *fs_info,

				  struct ulist *qgroups,

				  u64 nr_old_roots,

				  u64 nr_new_roots,

				  u64 num_bytes, u64 seq)

{

	struct ulist_node *unode;

	struct ulist_iterator uiter;

	struct btrfs_qgroup *qg;

	u64 cur_new_count, cur_old_count;



	ULIST_ITER_INIT(&uiter);

	while ((unode = ulist_next(qgroups, &uiter))) {

		bool dirty = false;



		qg = u64_to_ptr(unode->aux);

		cur_old_count = btrfs_qgroup_get_old_refcnt(qg, seq);

		cur_new_count = btrfs_qgroup_get_new_refcnt(qg, seq);



		/* Rfer update part */

		if (cur_old_count == 0 && cur_new_count > 0) {

			qg->rfer += num_bytes;

			qg->rfer_cmpr += num_bytes;

			dirty = true;

		}

		if (cur_old_count > 0 && cur_new_count == 0) {

			qg->rfer -= num_bytes;

			qg->rfer_cmpr -= num_bytes;

			dirty = true;

		}



		/* Excl update part */

		/* Exclusive/none -> shared case */

		if (cur_old_count == nr_old_roots &&

		    cur_new_count < nr_new_roots) {

			/* Exclusive -> shared */

			if (cur_old_count != 0) {

				qg->excl -= num_bytes;

				qg->excl_cmpr -= num_bytes;

				dirty = true;

			}

		}



		/* Shared -> exclusive/none case */

		if (cur_old_count < nr_old_roots &&

		    cur_new_count == nr_new_roots) {

			/* Shared->exclusive */

			if (cur_new_count != 0) {

				qg->excl += num_bytes;

				qg->excl_cmpr += num_bytes;

				dirty = true;

			}

		}



		/* Exclusive/none -> exclusive/none case */

		if (cur_old_count == nr_old_roots &&

		    cur_new_count == nr_new_roots) {

			if (cur_old_count == 0) {

				/* None -> exclusive/none */



				if (cur_new_count != 0) {

					/* None -> exclusive */

					qg->excl += num_bytes;

					qg->excl_cmpr += num_bytes;

					dirty = true;

				}

				/* None -> none, nothing changed */

			} else {

				/* Exclusive -> exclusive/none */



				if (cur_new_count == 0) {

					/* Exclusive -> none */

					qg->excl -= num_bytes;

					qg->excl_cmpr -= num_bytes;

					dirty = true;

				}

				/* Exclusive -> exclusive, nothing changed */

			}

		}

		if (dirty)

			qgroup_dirty(fs_info, qg);

	}

	return 0;

}



/*

 * This adjusts the counters for all referenced qgroups if need be.

 */