DragonFlyBSD

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