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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: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>
This commit is contained in:
Qu Wenruo 2015-04-12 16:59:57 +08:00 committed by Chris Mason
parent d810ef2be5
commit 823ae5b8e3
1 changed files with 120 additions and 0 deletions
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120
fs/btrfs/qgroup.c
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@ -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.
*/