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xfs: refactor and reuse best extent scanning logic 

The bnobt "find best" helper implements a simple btree walker
function. This general pattern, or a subset thereof, is reused in
various parts of a near mode allocation operation. For example, the
bnobt left/right scans are each iterative btree walks along with the
cntbt lastblock scan.

Rework this function into a generic btree walker, add a couple
parameters to control termination behavior from various contexts and
reuse it where applicable.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
This commit is contained in:
Brian Foster 2019-10-13 17:10:34 -07:00 committed by Darrick J. Wong
parent 4a65b7c2c7
commit 78d7aabdee
1 changed files with 55 additions and 55 deletions
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110
fs/xfs/libxfs/xfs_alloc.c
View File

@ -875,6 +875,13 @@ xfs_alloc_cur_check(
acur->diff = diff;
*new = 1;
/*
* We're done if we found a perfect allocation. This only deactivates
* the current cursor, but this is just an optimization to terminate a
* cntbt search that otherwise runs to the edge of the tree.
*/
if (acur->diff == 0 && acur->len == args->maxlen)
deactivate = true;
out:
if (deactivate)
cur->bc_private.a.priv.abt.active = false;
@ -1172,30 +1179,38 @@ error0:
}
/*
* Search the btree in a given direction and check the records against the good
* extent we've already found.
* Search a given number of btree records in a given direction. Check each
* record against the good extent we've already found.
*/
STATIC int
xfs_alloc_find_best_extent(
xfs_alloc_walk_iter(
struct xfs_alloc_arg *args,
struct xfs_alloc_cur *acur,
struct xfs_btree_cur *cur,
bool increment)
bool increment,
bool find_one, /* quit on first candidate */
int count, /* rec count (-1 for infinite) */
int *stat)
{
int error;
int i;
*stat = 0;
/*
* Search so long as the cursor is active or we find a better extent.
* The cursor is deactivated if it extends beyond the range of the
* current allocation candidate.
*/
while (xfs_alloc_cur_active(cur)) {
while (xfs_alloc_cur_active(cur) && count) {
error = xfs_alloc_cur_check(args, acur, cur, &i);
if (error)
return error;
if (i == 1)
break;
if (i == 1) {
*stat = 1;
if (find_one)
break;
}
if (!xfs_alloc_cur_active(cur))
break;
@ -1207,6 +1222,9 @@ xfs_alloc_find_best_extent(
return error;
if (i == 0)
cur->bc_private.a.priv.abt.active = false;
if (count > 0)
count--;
}
return 0;
@ -1226,7 +1244,6 @@ xfs_alloc_ag_vextent_near(
struct xfs_btree_cur *fbcur = NULL;
int error; /* error code */
int i; /* result code, temporary */
int j; /* result code, temporary */
xfs_agblock_t bno;
xfs_extlen_t len;
bool fbinc = false;
@ -1313,19 +1330,12 @@ restart:
if (!i)
break;
}
i = acur.cnt->bc_ptrs[0];
for (j = 1;
!error && j && xfs_alloc_cur_active(acur.cnt) &&
(acur.len < args->maxlen || acur.diff > 0);
error = xfs_btree_increment(acur.cnt, 0, &j)) {
/*
* For each entry, decide if it's better than
* the previous best entry.
*/
error = xfs_alloc_cur_check(args, &acur, acur.cnt, &i);
if (error)
goto out;
}
error = xfs_alloc_walk_iter(args, &acur, acur.cnt, true, false,
-1, &i);
if (error)
goto out;
/*
* It didn't work. We COULD be in a case where
* there's a good record somewhere, so try again.
@ -1357,49 +1367,39 @@ restart:
goto out;
/*
* Loop going left with the leftward cursor, right with the
* rightward cursor, until either both directions give up or
* we find an entry at least as big as minlen.
* Loop going left with the leftward cursor, right with the rightward
* cursor, until either both directions give up or we find an entry at
* least as big as minlen.
*/
do {
if (xfs_alloc_cur_active(acur.bnolt)) {
error = xfs_alloc_cur_check(args, &acur, acur.bnolt, &i);
if (error)
goto out;
if (i == 1) {
trace_xfs_alloc_cur_left(args);
fbcur = acur.bnogt;
fbinc = true;
break;
}
error = xfs_btree_decrement(acur.bnolt, 0, &i);
if (error)
goto out;
if (!i)
acur.bnolt->bc_private.a.priv.abt.active = false;
error = xfs_alloc_walk_iter(args, &acur, acur.bnolt, false,
true, 1, &i);
if (error)
goto out;
if (i == 1) {
trace_xfs_alloc_cur_left(args);
fbcur = acur.bnogt;
fbinc = true;
break;
}
if (xfs_alloc_cur_active(acur.bnogt)) {
error = xfs_alloc_cur_check(args, &acur, acur.bnogt, &i);
if (error)
goto out;
if (i == 1) {
trace_xfs_alloc_cur_right(args);
fbcur = acur.bnolt;
fbinc = false;
break;
}
error = xfs_btree_increment(acur.bnogt, 0, &i);
if (error)
goto out;
if (!i)
acur.bnogt->bc_private.a.priv.abt.active = false;
error = xfs_alloc_walk_iter(args, &acur, acur.bnogt, true, true,
1, &i);
if (error)
goto out;
if (i == 1) {
trace_xfs_alloc_cur_right(args);
fbcur = acur.bnolt;
fbinc = false;
break;
}
} while (xfs_alloc_cur_active(acur.bnolt) ||
xfs_alloc_cur_active(acur.bnogt));
/* search the opposite direction for a better entry */
if (fbcur) {
error = xfs_alloc_find_best_extent(args, &acur, fbcur, fbinc);
error = xfs_alloc_walk_iter(args, &acur, fbcur, fbinc, true, -1,
&i);
if (error)
goto out;
}