[DragonFlyBSD - Submit #2842] (New) [PATCH] sys/vfs/hammer: Don't ex-lock all children on internal split

[bugtracker-admin at leaf.dragonflybsd.org]

Issue #2842 has been reported by tkusumi.

----------------------------------------
Submit #2842: [PATCH] sys/vfs/hammer: Don't ex-lock all children on internal split
http://bugs.dragonflybsd.org/issues/2842

* Author: tkusumi
* Status: New
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
----------------------------------------
Matt, please review this.
The diff is also attached to this PR.


=====
Date: Sun, 6 Sep 2015 00:17:00 +0900
Subject: [PATCH] sys/vfs/hammer: Don't ex-lock all children on internal split

hammer_split_internal() ex-locks all children of the node
to split via hammer_btree_lock_children(), but it actually
only needs to lock children at (index >= split).

Children at (index >= 0 && index < split) are not touched
by internal split and don't get affected by this operation.
In the following example, internal split does nothing to
E with * and their child nodes.

This commit adds an extra argument int start_index to
hammer_btree_lock_children() to specify from which child
this function needs to ex-lock.

=====
before split
I
0 1 2 3 ...     n
E E E E E E E E E R
           /
          /
         I                 62
         0 ... s ...     61|
         E E E E ... E E E R
         * * *

=====
after split
I                 n+1
0 1 2 3 ...   p   |
E E E E E E E E E E R
           /   \
          /     \
         I       \
         0 ... s  \
         E E E R   \
         * * *      I
                    0 1 2 ...
                    E E E ... R
---
 sys/vfs/hammer/hammer.h           |  1 +
 sys/vfs/hammer/hammer_btree.c     | 20 +++++++++++---------
 sys/vfs/hammer/hammer_rebalance.c |  2 +-
 sys/vfs/hammer/hammer_reblock.c   |  2 +-
 4 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/sys/vfs/hammer/hammer.h b/sys/vfs/hammer/hammer.h
index c47889f..b35f2e9 100644
--- a/sys/vfs/hammer/hammer.h
+++ b/sys/vfs/hammer/hammer.h
@@ -1265,6 +1265,7 @@ void	hammer_btree_lcache_init(hammer_mount_t hmp, hammer_node_lock_t lcache,
 			int depth);
 void	hammer_btree_lcache_free(hammer_mount_t hmp, hammer_node_lock_t lcache);
 int	hammer_btree_lock_children(hammer_cursor_t cursor, int depth,
+			int start_index,
 			hammer_node_lock_t parent,
 			hammer_node_lock_t lcache);
 void	hammer_btree_lock_copy(hammer_cursor_t cursor,
diff --git a/sys/vfs/hammer/hammer_btree.c b/sys/vfs/hammer/hammer_btree.c
index a34e6ca..cbd356a 100644
--- a/sys/vfs/hammer/hammer_btree.c
+++ b/sys/vfs/hammer/hammer_btree.c
@@ -1450,13 +1450,8 @@ btree_split_internal(hammer_cursor_t cursor)
 	int i;
 	const int esize = sizeof(*elm);
 
-	hammer_node_lock_init(&lockroot, cursor->node);
-	error = hammer_btree_lock_children(cursor, 1, &lockroot, NULL);
-	if (error)
-		goto done;
 	if ((error = hammer_cursor_upgrade(cursor)) != 0)
-		goto done;
-	++hammer_stats_btree_splits;
+		return(error);
 
 	/*
 	 * Calculate the split point.  If the insertion point is at the
@@ -1485,6 +1480,12 @@ btree_split_internal(hammer_cursor_t cursor)
 			--split;
 	}
 
+	hammer_node_lock_init(&lockroot, cursor->node);
+	error = hammer_btree_lock_children(cursor, 1, split, &lockroot, NULL);
+	if (error)
+		goto done;
+	++hammer_stats_btree_splits;
+
 	/*
 	 * If we are at the root of the filesystem, create a new root node
 	 * with 1 element and split normally.  Avoid making major
@@ -2631,7 +2632,7 @@ hammer_btree_lcache_free(hammer_mount_t hmp, hammer_node_lock_t lcache)
  * is usually aliased from a cursor.
  */
 int
-hammer_btree_lock_children(hammer_cursor_t cursor, int depth,
+hammer_btree_lock_children(hammer_cursor_t cursor, int depth, int start_index,
 			   hammer_node_lock_t parent,
 			   hammer_node_lock_t lcache)
 {
@@ -2657,7 +2658,7 @@ hammer_btree_lock_children(hammer_cursor_t cursor, int depth,
 	 * pre-get the children before trying to lock the mess.  This is
 	 * only done one-level deep for now.
 	 */
-	for (i = 0; i < ondisk->count; ++i) {
+	for (i = start_index; i < ondisk->count; ++i) {
 		++hammer_stats_btree_elements;
 		elm = &ondisk->elms[i];
 		child = hammer_get_node(cursor->trans,
@@ -2670,7 +2671,7 @@ hammer_btree_lock_children(hammer_cursor_t cursor, int depth,
 	/*
 	 * Do it for real
 	 */
-	for (i = 0; error == 0 && i < ondisk->count; ++i) {
+	for (i = start_index; error == 0 && i < ondisk->count; ++i) {
 		++hammer_stats_btree_elements;
 		elm = &ondisk->elms[i];
 
@@ -2712,6 +2713,7 @@ hammer_btree_lock_children(hammer_cursor_t cursor, int depth,
 					error = hammer_btree_lock_children(
 							cursor,
 							depth - 1,
+							0,
 							item,
 							lcache);
 				}
diff --git a/sys/vfs/hammer/hammer_rebalance.c b/sys/vfs/hammer/hammer_rebalance.c
index 28247bd..0788d6d 100644
--- a/sys/vfs/hammer/hammer_rebalance.c
+++ b/sys/vfs/hammer/hammer_rebalance.c
@@ -285,7 +285,7 @@ rebalance_node(struct hammer_ioc_rebalance *rebal, hammer_cursor_t cursor,
 	error = hammer_cursor_upgrade(cursor);
 	if (error)
 		goto done;
-	error = hammer_btree_lock_children(cursor, 2, &lockroot, lcache);
+	error = hammer_btree_lock_children(cursor, 2, 0, &lockroot, lcache);
 	if (error)
 		goto done;
 
diff --git a/sys/vfs/hammer/hammer_reblock.c b/sys/vfs/hammer/hammer_reblock.c
index 21aef3d..c002367 100644
--- a/sys/vfs/hammer/hammer_reblock.c
+++ b/sys/vfs/hammer/hammer_reblock.c
@@ -571,7 +571,7 @@ hammer_reblock_int_node(struct hammer_ioc_reblock *reblock,
 	int error;
 
 	hammer_node_lock_init(&lockroot, cursor->node);
-	error = hammer_btree_lock_children(cursor, 1, &lockroot, NULL);
+	error = hammer_btree_lock_children(cursor, 1, 0, &lockroot, NULL);
 	if (error)
 		goto done;
 
-- 
2.4.6



---Files--------------------------------
0001-sys-vfs-hammer-Don-t-ex-lock-all-children-on-interna.patch (5.16 KB)


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