xfs: exact busy extent tracking
Update the extent tree in case we have to reuse a busy extent, so that it
always is kept uptodate. This is done by replacing the busy list searches
with a new xfs_alloc_busy_reuse helper, which updates the busy extent tree
in case of a reuse. This allows us to allow reusing metadata extents
unconditionally, and thus avoid log forces especially for allocation btree
blocks.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
diff --git a/fs/xfs/xfs_alloc.c b/fs/xfs/xfs_alloc.c
index ff54ef4..53157d4 100644
--- a/fs/xfs/xfs_alloc.c
+++ b/fs/xfs/xfs_alloc.c
@@ -1396,8 +1396,9 @@
if (error)
goto error0;
if (fbno != NULLAGBLOCK) {
- if (xfs_alloc_busy_search(args->mp, args->agno, fbno, 1))
- xfs_trans_set_sync(args->tp);
+ xfs_alloc_busy_reuse(args->mp, args->agno, fbno, 1,
+ args->userdata);
+
if (args->userdata) {
xfs_buf_t *bp;
@@ -2475,100 +2476,6 @@
return error;
}
-
-/*
- * AG Busy list management
- * The busy list contains block ranges that have been freed but whose
- * transactions have not yet hit disk. If any block listed in a busy
- * list is reused, the transaction that freed it must be forced to disk
- * before continuing to use the block.
- *
- * xfs_alloc_busy_insert - add to the per-ag busy list
- * xfs_alloc_busy_clear - remove an item from the per-ag busy list
- * xfs_alloc_busy_search - search for a busy extent
- */
-
-/*
- * Insert a new extent into the busy tree.
- *
- * The busy extent tree is indexed by the start block of the busy extent.
- * there can be multiple overlapping ranges in the busy extent tree but only
- * ever one entry at a given start block. The reason for this is that
- * multi-block extents can be freed, then smaller chunks of that extent
- * allocated and freed again before the first transaction commit is on disk.
- * If the exact same start block is freed a second time, we have to wait for
- * that busy extent to pass out of the tree before the new extent is inserted.
- * There are two main cases we have to handle here.
- *
- * The first case is a transaction that triggers a "free - allocate - free"
- * cycle. This can occur during btree manipulations as a btree block is freed
- * to the freelist, then allocated from the free list, then freed again. In
- * this case, the second extxpnet free is what triggers the duplicate and as
- * such the transaction IDs should match. Because the extent was allocated in
- * this transaction, the transaction must be marked as synchronous. This is
- * true for all cases where the free/alloc/free occurs in the one transaction,
- * hence the addition of the ASSERT(tp->t_flags & XFS_TRANS_SYNC) to this case.
- * This serves to catch violations of the second case quite effectively.
- *
- * The second case is where the free/alloc/free occur in different
- * transactions. In this case, the thread freeing the extent the second time
- * can't mark the extent busy immediately because it is already tracked in a
- * transaction that may be committing. When the log commit for the existing
- * busy extent completes, the busy extent will be removed from the tree. If we
- * allow the second busy insert to continue using that busy extent structure,
- * it can be freed before this transaction is safely in the log. Hence our
- * only option in this case is to force the log to remove the existing busy
- * extent from the list before we insert the new one with the current
- * transaction ID.
- *
- * The problem we are trying to avoid in the free-alloc-free in separate
- * transactions is most easily described with a timeline:
- *
- * Thread 1 Thread 2 Thread 3 xfslogd
- * xact alloc
- * free X
- * mark busy
- * commit xact
- * free xact
- * xact alloc
- * alloc X
- * busy search
- * mark xact sync
- * commit xact
- * free xact
- * force log
- * checkpoint starts
- * ....
- * xact alloc
- * free X
- * mark busy
- * finds match
- * *** KABOOM! ***
- * ....
- * log IO completes
- * unbusy X
- * checkpoint completes
- *
- * By issuing a log force in thread 3 @ "KABOOM", the thread will block until
- * the checkpoint completes, and the busy extent it matched will have been
- * removed from the tree when it is woken. Hence it can then continue safely.
- *
- * However, to ensure this matching process is robust, we need to use the
- * transaction ID for identifying transaction, as delayed logging results in
- * the busy extent and transaction lifecycles being different. i.e. the busy
- * extent is active for a lot longer than the transaction. Hence the
- * transaction structure can be freed and reallocated, then mark the same
- * extent busy again in the new transaction. In this case the new transaction
- * will have a different tid but can have the same address, and hence we need
- * to check against the tid.
- *
- * Future: for delayed logging, we could avoid the log force if the extent was
- * first freed in the current checkpoint sequence. This, however, requires the
- * ability to pin the current checkpoint in memory until this transaction
- * commits to ensure that both the original free and the current one combine
- * logically into the one checkpoint. If the checkpoint sequences are
- * different, however, we still need to wait on a log force.
- */
void
xfs_alloc_busy_insert(
struct xfs_trans *tp,
@@ -2580,9 +2487,7 @@
struct xfs_busy_extent *busyp;
struct xfs_perag *pag;
struct rb_node **rbp;
- struct rb_node *parent;
- int match;
-
+ struct rb_node *parent = NULL;
new = kmem_zalloc(sizeof(struct xfs_busy_extent), KM_MAYFAIL);
if (!new) {
@@ -2591,7 +2496,7 @@
* block, make this a synchronous transaction to insure that
* the block is not reused before this transaction commits.
*/
- trace_xfs_alloc_busy(tp, agno, bno, len, 1);
+ trace_xfs_alloc_busy_enomem(tp->t_mountp, agno, bno, len);
xfs_trans_set_sync(tp);
return;
}
@@ -2599,66 +2504,28 @@
new->agno = agno;
new->bno = bno;
new->length = len;
- new->tid = xfs_log_get_trans_ident(tp);
-
INIT_LIST_HEAD(&new->list);
/* trace before insert to be able to see failed inserts */
- trace_xfs_alloc_busy(tp, agno, bno, len, 0);
+ trace_xfs_alloc_busy(tp->t_mountp, agno, bno, len);
pag = xfs_perag_get(tp->t_mountp, new->agno);
-restart:
spin_lock(&pag->pagb_lock);
rbp = &pag->pagb_tree.rb_node;
- parent = NULL;
- busyp = NULL;
- match = 0;
- while (*rbp && match >= 0) {
+ while (*rbp) {
parent = *rbp;
busyp = rb_entry(parent, struct xfs_busy_extent, rb_node);
if (new->bno < busyp->bno) {
- /* may overlap, but exact start block is lower */
rbp = &(*rbp)->rb_left;
- if (new->bno + new->length > busyp->bno)
- match = busyp->tid == new->tid ? 1 : -1;
+ ASSERT(new->bno + new->length <= busyp->bno);
} else if (new->bno > busyp->bno) {
- /* may overlap, but exact start block is higher */
rbp = &(*rbp)->rb_right;
- if (bno < busyp->bno + busyp->length)
- match = busyp->tid == new->tid ? 1 : -1;
+ ASSERT(bno >= busyp->bno + busyp->length);
} else {
- match = busyp->tid == new->tid ? 1 : -1;
- break;
+ ASSERT(0);
}
}
- if (match < 0) {
- /* overlap marked busy in different transaction */
- spin_unlock(&pag->pagb_lock);
- xfs_log_force(tp->t_mountp, XFS_LOG_SYNC);
- goto restart;
- }
- if (match > 0) {
- /*
- * overlap marked busy in same transaction. Update if exact
- * start block match, otherwise combine the busy extents into
- * a single range.
- */
- if (busyp->bno == new->bno) {
- busyp->length = max(busyp->length, new->length);
- spin_unlock(&pag->pagb_lock);
- ASSERT(tp->t_flags & XFS_TRANS_SYNC);
- xfs_perag_put(pag);
- kmem_free(new);
- return;
- }
- rb_erase(&busyp->rb_node, &pag->pagb_tree);
- new->length = max(busyp->bno + busyp->length,
- new->bno + new->length) -
- min(busyp->bno, new->bno);
- new->bno = min(busyp->bno, new->bno);
- } else
- busyp = NULL;
rb_link_node(&new->rb_node, parent, rbp);
rb_insert_color(&new->rb_node, &pag->pagb_tree);
@@ -2666,7 +2533,6 @@
list_add(&new->list, &tp->t_busy);
spin_unlock(&pag->pagb_lock);
xfs_perag_put(pag);
- kmem_free(busyp);
}
/*
@@ -2715,12 +2581,196 @@
}
}
spin_unlock(&pag->pagb_lock);
- trace_xfs_alloc_busysearch(mp, agno, bno, len, !!match);
xfs_perag_put(pag);
return match;
}
/*
+ * The found free extent [fbno, fend] overlaps part or all of the given busy
+ * extent. If the overlap covers the beginning, the end, or all of the busy
+ * extent, the overlapping portion can be made unbusy and used for the
+ * allocation. We can't split a busy extent because we can't modify a
+ * transaction/CIL context busy list, but we can update an entries block
+ * number or length.
+ *
+ * Returns true if the extent can safely be reused, or false if the search
+ * needs to be restarted.
+ */
+STATIC bool
+xfs_alloc_busy_update_extent(
+ struct xfs_mount *mp,
+ struct xfs_perag *pag,
+ struct xfs_busy_extent *busyp,
+ xfs_agblock_t fbno,
+ xfs_extlen_t flen,
+ bool userdata)
+{
+ xfs_agblock_t fend = fbno + flen;
+ xfs_agblock_t bbno = busyp->bno;
+ xfs_agblock_t bend = bbno + busyp->length;
+
+ /*
+ * If there is a busy extent overlapping a user allocation, we have
+ * no choice but to force the log and retry the search.
+ *
+ * Fortunately this does not happen during normal operation, but
+ * only if the filesystem is very low on space and has to dip into
+ * the AGFL for normal allocations.
+ */
+ if (userdata)
+ goto out_force_log;
+
+ if (bbno < fbno && bend > fend) {
+ /*
+ * Case 1:
+ * bbno bend
+ * +BBBBBBBBBBBBBBBBB+
+ * +---------+
+ * fbno fend
+ */
+
+ /*
+ * We would have to split the busy extent to be able to track
+ * it correct, which we cannot do because we would have to
+ * modify the list of busy extents attached to the transaction
+ * or CIL context, which is immutable.
+ *
+ * Force out the log to clear the busy extent and retry the
+ * search.
+ */
+ goto out_force_log;
+ } else if (bbno >= fbno && bend <= fend) {
+ /*
+ * Case 2:
+ * bbno bend
+ * +BBBBBBBBBBBBBBBBB+
+ * +-----------------+
+ * fbno fend
+ *
+ * Case 3:
+ * bbno bend
+ * +BBBBBBBBBBBBBBBBB+
+ * +--------------------------+
+ * fbno fend
+ *
+ * Case 4:
+ * bbno bend
+ * +BBBBBBBBBBBBBBBBB+
+ * +--------------------------+
+ * fbno fend
+ *
+ * Case 5:
+ * bbno bend
+ * +BBBBBBBBBBBBBBBBB+
+ * +-----------------------------------+
+ * fbno fend
+ *
+ */
+
+ /*
+ * The busy extent is fully covered by the extent we are
+ * allocating, and can simply be removed from the rbtree.
+ * However we cannot remove it from the immutable list
+ * tracking busy extents in the transaction or CIL context,
+ * so set the length to zero to mark it invalid.
+ *
+ * We also need to restart the busy extent search from the
+ * tree root, because erasing the node can rearrange the
+ * tree topology.
+ */
+ rb_erase(&busyp->rb_node, &pag->pagb_tree);
+ busyp->length = 0;
+ return false;
+ } else if (fend < bend) {
+ /*
+ * Case 6:
+ * bbno bend
+ * +BBBBBBBBBBBBBBBBB+
+ * +---------+
+ * fbno fend
+ *
+ * Case 7:
+ * bbno bend
+ * +BBBBBBBBBBBBBBBBB+
+ * +------------------+
+ * fbno fend
+ *
+ */
+ busyp->bno = fend;
+ } else if (bbno < fbno) {
+ /*
+ * Case 8:
+ * bbno bend
+ * +BBBBBBBBBBBBBBBBB+
+ * +-------------+
+ * fbno fend
+ *
+ * Case 9:
+ * bbno bend
+ * +BBBBBBBBBBBBBBBBB+
+ * +----------------------+
+ * fbno fend
+ */
+ busyp->length = fbno - busyp->bno;
+ } else {
+ ASSERT(0);
+ }
+
+ trace_xfs_alloc_busy_reuse(mp, pag->pag_agno, fbno, flen);
+ return true;
+
+out_force_log:
+ spin_unlock(&pag->pagb_lock);
+ xfs_log_force(mp, XFS_LOG_SYNC);
+ trace_xfs_alloc_busy_force(mp, pag->pag_agno, fbno, flen);
+ spin_lock(&pag->pagb_lock);
+ return false;
+}
+
+
+/*
+ * For a given extent [fbno, flen], make sure we can reuse it safely.
+ */
+void
+xfs_alloc_busy_reuse(
+ struct xfs_mount *mp,
+ xfs_agnumber_t agno,
+ xfs_agblock_t fbno,
+ xfs_extlen_t flen,
+ bool userdata)
+{
+ struct xfs_perag *pag;
+ struct rb_node *rbp;
+
+ ASSERT(flen > 0);
+
+ pag = xfs_perag_get(mp, agno);
+ spin_lock(&pag->pagb_lock);
+restart:
+ rbp = pag->pagb_tree.rb_node;
+ while (rbp) {
+ struct xfs_busy_extent *busyp =
+ rb_entry(rbp, struct xfs_busy_extent, rb_node);
+ xfs_agblock_t bbno = busyp->bno;
+ xfs_agblock_t bend = bbno + busyp->length;
+
+ if (fbno + flen <= bbno) {
+ rbp = rbp->rb_left;
+ continue;
+ } else if (fbno >= bend) {
+ rbp = rbp->rb_right;
+ continue;
+ }
+
+ if (!xfs_alloc_busy_update_extent(mp, pag, busyp, fbno, flen,
+ userdata))
+ goto restart;
+ }
+ spin_unlock(&pag->pagb_lock);
+ xfs_perag_put(pag);
+}
+
+/*
* For a given extent [fbno, flen], search the busy extent list to find a
* subset of the extent that is not busy. If *rlen is smaller than
* args->minlen no suitable extent could be found, and the higher level
@@ -2734,13 +2784,16 @@
xfs_agblock_t *rbno,
xfs_extlen_t *rlen)
{
- xfs_agblock_t fbno = bno;
- xfs_extlen_t flen = len;
+ xfs_agblock_t fbno;
+ xfs_extlen_t flen;
struct rb_node *rbp;
- ASSERT(flen > 0);
+ ASSERT(len > 0);
spin_lock(&args->pag->pagb_lock);
+restart:
+ fbno = bno;
+ flen = len;
rbp = args->pag->pagb_tree.rb_node;
while (rbp && flen >= args->minlen) {
struct xfs_busy_extent *busyp =
@@ -2757,6 +2810,18 @@
continue;
}
+ /*
+ * If this is a metadata allocation, try to reuse the busy
+ * extent instead of trimming the allocation.
+ */
+ if (!args->userdata) {
+ if (!xfs_alloc_busy_update_extent(args->mp, args->pag,
+ busyp, fbno, flen,
+ false))
+ goto restart;
+ continue;
+ }
+
if (bbno <= fbno) {
/* start overlap */
@@ -2906,17 +2971,15 @@
{
struct xfs_perag *pag;
- trace_xfs_alloc_unbusy(mp, busyp->agno, busyp->bno,
- busyp->length);
-
- ASSERT(xfs_alloc_busy_search(mp, busyp->agno, busyp->bno,
- busyp->length) == 1);
-
list_del_init(&busyp->list);
pag = xfs_perag_get(mp, busyp->agno);
spin_lock(&pag->pagb_lock);
- rb_erase(&busyp->rb_node, &pag->pagb_tree);
+ if (busyp->length) {
+ trace_xfs_alloc_busy_clear(mp, busyp->agno, busyp->bno,
+ busyp->length);
+ rb_erase(&busyp->rb_node, &pag->pagb_tree);
+ }
spin_unlock(&pag->pagb_lock);
xfs_perag_put(pag);