struct xfs_btree_cur *cnt; /* btree cursors */
struct xfs_btree_cur *bnolt;
struct xfs_btree_cur *bnogt;
+ xfs_extlen_t cur_len;/* current search length */
xfs_agblock_t rec_bno;/* extent startblock */
xfs_extlen_t rec_len;/* extent length */
xfs_agblock_t bno; /* alloc bno */
ASSERT(args->alignment == 1 || args->type != XFS_ALLOCTYPE_THIS_BNO);
+ acur->cur_len = args->maxlen;
acur->rec_bno = 0;
acur->rec_len = 0;
acur->bno = 0;
}
/*
+ * Locality allocation lookup algorithm. This expects a cntbt cursor and uses
+ * bno optimized lookup to search for extents with ideal size and locality.
+ */
+STATIC int
+xfs_alloc_cntbt_iter(
+ struct xfs_alloc_arg *args,
+ struct xfs_alloc_cur *acur)
+{
+ struct xfs_btree_cur *cur = acur->cnt;
+ xfs_agblock_t bno;
+ xfs_extlen_t len, cur_len;
+ int error;
+ int i;
+
+ if (!xfs_alloc_cur_active(cur))
+ return 0;
+
+ /* locality optimized lookup */
+ cur_len = acur->cur_len;
+ error = xfs_alloc_lookup_ge(cur, args->agbno, cur_len, &i);
+ if (error)
+ return error;
+ if (i == 0)
+ return 0;
+ error = xfs_alloc_get_rec(cur, &bno, &len, &i);
+ if (error)
+ return error;
+
+ /* check the current record and update search length from it */
+ error = xfs_alloc_cur_check(args, acur, cur, &i);
+ if (error)
+ return error;
+ ASSERT(len >= acur->cur_len);
+ acur->cur_len = len;
+
+ /*
+ * We looked up the first record >= [agbno, len] above. The agbno is a
+ * secondary key and so the current record may lie just before or after
+ * agbno. If it is past agbno, check the previous record too so long as
+ * the length matches as it may be closer. Don't check a smaller record
+ * because that could deactivate our cursor.
+ */
+ if (bno > args->agbno) {
+ error = xfs_btree_decrement(cur, 0, &i);
+ if (!error && i) {
+ error = xfs_alloc_get_rec(cur, &bno, &len, &i);
+ if (!error && i && len == acur->cur_len)
+ error = xfs_alloc_cur_check(args, acur, cur,
+ &i);
+ }
+ if (error)
+ return error;
+ }
+
+ /*
+ * Increment the search key until we find at least one allocation
+ * candidate or if the extent we found was larger. Otherwise, double the
+ * search key to optimize the search. Efficiency is more important here
+ * than absolute best locality.
+ */
+ cur_len <<= 1;
+ if (!acur->len || acur->cur_len >= cur_len)
+ acur->cur_len++;
+ else
+ acur->cur_len = cur_len;
+
+ return error;
+}
+
+/*
* Deal with the case where only small freespaces remain. Either return the
* contents of the last freespace record, or allocate space from the freelist if
* there is nothing in the tree.
}
/*
- * Search in the by-bno btree to the left and to the right simultaneously until
- * in each case we find a large enough free extent or run into the edge of the
- * tree. When we run into the edge of the tree, we deactivate that cursor.
+ * Search the by-bno and by-size btrees in parallel in search of an extent with
+ * ideal locality based on the NEAR mode ->agbno locality hint.
*/
STATIC int
-xfs_alloc_ag_vextent_bnobt(
+xfs_alloc_ag_vextent_locality(
struct xfs_alloc_arg *args,
struct xfs_alloc_cur *acur,
int *stat)
*stat = 0;
+ error = xfs_alloc_lookup_ge(acur->cnt, args->agbno, acur->cur_len, &i);
+ if (error)
+ return error;
error = xfs_alloc_lookup_le(acur->bnolt, args->agbno, 0, &i);
if (error)
return error;
return error;
/*
- * 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.
+ * Search the bnobt and cntbt in parallel. Search the bnobt left and
+ * right and lookup the closest extent to the locality hint for each
+ * extent size key in the cntbt. The entire search terminates
+ * immediately on a bnobt hit because that means we've found best case
+ * locality. Otherwise the search continues until the cntbt cursor runs
+ * off the end of the tree. If no allocation candidate is found at this
+ * point, give up on locality, walk backwards from the end of the cntbt
+ * and take the first available extent.
+ *
+ * The parallel tree searches balance each other out to provide fairly
+ * consistent performance for various situations. The bnobt search can
+ * have pathological behavior in the worst case scenario of larger
+ * allocation requests and fragmented free space. On the other hand, the
+ * bnobt is able to satisfy most smaller allocation requests much more
+ * quickly than the cntbt. The cntbt search can sift through fragmented
+ * free space and sets of free extents for larger allocation requests
+ * more quickly than the bnobt. Since the locality hint is just a hint
+ * and we don't want to scan the entire bnobt for perfect locality, the
+ * cntbt search essentially bounds the bnobt search such that we can
+ * find good enough locality at reasonable performance in most cases.
*/
while (xfs_alloc_cur_active(acur->bnolt) ||
- xfs_alloc_cur_active(acur->bnogt)) {
+ xfs_alloc_cur_active(acur->bnogt) ||
+ xfs_alloc_cur_active(acur->cnt)) {
+
+ trace_xfs_alloc_cur_lookup(args);
+
+ /*
+ * Search the bnobt left and right. In the case of a hit, finish
+ * the search in the opposite direction and we're done.
+ */
error = xfs_alloc_walk_iter(args, acur, acur->bnolt, false,
true, 1, &i);
if (error)
fbinc = true;
break;
}
-
error = xfs_alloc_walk_iter(args, acur, acur->bnogt, true, true,
1, &i);
if (error)
fbinc = false;
break;
}
+
+ /*
+ * Check the extent with best locality based on the current
+ * extent size search key and keep track of the best candidate.
+ */
+ error = xfs_alloc_cntbt_iter(args, acur);
+ if (error)
+ return error;
+ if (!xfs_alloc_cur_active(acur->cnt)) {
+ trace_xfs_alloc_cur_lookup_done(args);
+ break;
+ }
+ }
+
+ /*
+ * If we failed to find anything due to busy extents, return empty
+ * handed so the caller can flush and retry. If no busy extents were
+ * found, walk backwards from the end of the cntbt as a last resort.
+ */
+ if (!xfs_alloc_cur_active(acur->cnt) && !acur->len && !acur->busy) {
+ error = xfs_btree_decrement(acur->cnt, 0, &i);
+ if (error)
+ return error;
+ if (i) {
+ acur->cnt->bc_private.a.priv.abt.active = true;
+ fbcur = acur->cnt;
+ fbinc = false;
+ }
}
- /* search the opposite direction for a better entry */
+ /*
+ * Search in the opposite direction for a better entry in the case of
+ * a bnobt hit or walk backwards from the end of the cntbt.
+ */
if (fbcur) {
error = xfs_alloc_walk_iter(args, acur, fbcur, fbinc, true, -1,
&i);
}
/*
- * Second algorithm. Search the bnobt left and right.
+ * Second algorithm. Combined cntbt and bnobt search to find ideal
+ * locality.
*/
- error = xfs_alloc_ag_vextent_bnobt(args, &acur, &i);
+ error = xfs_alloc_ag_vextent_locality(args, &acur, &i);
if (error)
goto out;
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