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Btrfs: Reduce contention on the root node 

This calls unlock_up sooner in btrfs_search_slot in order to decrease the
amount of work done with the higher level tree locks held.

Also, it changes btrfs_tree_lock to spin for a big against the page lock
before scheduling.  This makes a big difference in context switch rate under
highly contended workloads.

Longer term, a better locking structure is needed than the page lock.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
This commit is contained in:
Chris Mason 2008-06-25 16:14:04 -04:00
parent 3f157a2fd2
commit f9efa9c784
2 changed files with 21 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

17
fs/btrfs/ctree.c
View File

@ -1313,16 +1313,13 @@ again:
slot = p->slots[level];
BUG_ON(btrfs_header_nritems(b) == 1);
}
unlock_up(p, level, lowest_unlock);
/* this is only true while dropping a snapshot */
if (level == lowest_level) {
unlock_up(p, level, lowest_unlock);
break;
}
if (should_reada)
reada_for_search(root, p, level, slot,
key->objectid);
blocknr = btrfs_node_blockptr(b, slot);
gen = btrfs_node_ptr_generation(b, slot);
blocksize = btrfs_level_size(root, level - 1);
@ -1340,6 +1337,11 @@ again:
btrfs_release_path(NULL, p);
if (tmp)
free_extent_buffer(tmp);
if (should_reada)
reada_for_search(root, p,
level, slot,
key->objectid);
tmp = read_tree_block(root, blocknr,
blocksize, gen);
if (tmp)
@ -1348,12 +1350,15 @@ again:
} else {
if (tmp)
free_extent_buffer(tmp);
if (should_reada)
reada_for_search(root, p,
level, slot,
key->objectid);
b = read_node_slot(root, b, slot);
}
}
if (!p->skip_locking)
btrfs_tree_lock(b);
unlock_up(p, level, lowest_unlock);
} else {
p->slots[level] = slot;
if (ins_len > 0 && btrfs_leaf_free_space(root, b) <

10
fs/btrfs/locking.c
View File

@ -27,6 +27,16 @@
int btrfs_tree_lock(struct extent_buffer *eb)
{
int i;
if (!TestSetPageLocked(eb->first_page))
return 0;
for (i = 0; i < 512; i++) {
cpu_relax();
if (!TestSetPageLocked(eb->first_page))
return 0;
}
cpu_relax();
lock_page(eb->first_page);
return 0;
}