| Message ID | 1526612424-97061-6-git-send-email-bo.liu@linux.alibaba.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, May 18, 2018 at 11:00:23AM +0800, Liu Bo wrote: > Typically, when acquiring root node's lock, btrfs tries its best to get > read lock and trade for write lock if @write_lock_level implies to do so. > > In case of (cow && (p->keep_locks || p->lowest_level)), write_lock_level > is set to BTRFS_MAX_LEVEL, which means we need to acquire root node's > write lock directly. > > In this particular case, the dance of acquiring read lock and then trading > for write lock can be saved. > > Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com> Reviewed-by: David Sterba <dsterba@suse.com> > --- > fs/btrfs/ctree.c | 29 ++++++++++++++++------------- > 1 file changed, 16 insertions(+), 13 deletions(-) > > diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c > index 8d3b09038f37..e619f7e01794 100644 > --- a/fs/btrfs/ctree.c > +++ b/fs/btrfs/ctree.c > @@ -2633,20 +2633,23 @@ static struct extent_buffer *btrfs_search_slot_get_root(struct btrfs_root *root, > goto out; > } > > - /* > - * we don't know the level of the root node until we actually > - * have it read locked > - */ > - b = btrfs_read_lock_root_node(root); > - level = btrfs_header_level(b); > - if (level > write_lock_level) > - goto out; I've added a comment why the check below is done. > + if (write_lock_level < BTRFS_MAX_LEVEL) { -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c index 8d3b09038f37..e619f7e01794 100644 --- a/fs/btrfs/ctree.c +++ b/fs/btrfs/ctree.c @@ -2633,20 +2633,23 @@ static struct extent_buffer *btrfs_search_slot_get_root(struct btrfs_root *root, goto out; } - /* - * we don't know the level of the root node until we actually - * have it read locked - */ - b = btrfs_read_lock_root_node(root); - level = btrfs_header_level(b); - if (level > write_lock_level) - goto out; + if (write_lock_level < BTRFS_MAX_LEVEL) { + /* + * we don't know the level of the root node until we actually + * have it read locked + */ + b = btrfs_read_lock_root_node(root); + level = btrfs_header_level(b); + if (level > write_lock_level) + goto out; + + /* + * whoops, must trade for write lock + */ + btrfs_tree_read_unlock(b); + free_extent_buffer(b); + } - /* - * whoops, must trade for write lock - */ - btrfs_tree_read_unlock(b); - free_extent_buffer(b); b = btrfs_lock_root_node(root); root_lock = BTRFS_WRITE_LOCK; /*
Typically, when acquiring root node's lock, btrfs tries its best to get read lock and trade for write lock if @write_lock_level implies to do so. In case of (cow && (p->keep_locks || p->lowest_level)), write_lock_level is set to BTRFS_MAX_LEVEL, which means we need to acquire root node's write lock directly. In this particular case, the dance of acquiring read lock and then trading for write lock can be saved. Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com> --- fs/btrfs/ctree.c | 29 ++++++++++++++++------------- 1 file changed, 16 insertions(+), 13 deletions(-)