On Thu, Aug 22, 2013 at 05:04:59AM +0900, Ryusuke Konishi wrote:
> On Wed, 21 Aug 2013 06:40:56 +0100, Al Viro wrote:
> > And I would like to understand what nilfs one is trying to do...
> > Unless I'm seriously misreading that code, it's *not* on any kind of a hot
> > path, so I really wonder why don't we simply do shrink_dcache_parent() +
> > check if d_count has dropped to 1, without trying to look for submounts
> > first - if we have any, shrink_dcache_parent() is simply going to leave
> > us with d_count > 1 and that's it. Actually, it's cheaper that way -
> > no need to walk the tree twice.
>
> > We are really getting too many tree walkers in fs/dcache.c and
> > all that duplication is the prime breeding ground for bugs ;-/
>
> I agree that we can eliminate have_submounts() from nilfs. Please
> apply the following patch if you hope so.
>
> > Moreover, checking for d_count == 1
> > case first is also pointless - in that case we have no children at all
> > and shrink_dcache_parent() will return immediately.
>
> This also looks true. I will confirm whether we can remove the
> pre-check for d_count == 1 case.
Umm... How about the following, then?
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index af3ba04..7ac2a12 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -994,23 +994,16 @@ static int nilfs_attach_snapshot(struct super_block *s, __u64 cno,
return ret;
}
-static int nilfs_tree_was_touched(struct dentry *root_dentry)
-{
- return d_count(root_dentry) > 1;
-}
-
/**
- * nilfs_try_to_shrink_tree() - try to shrink dentries of a checkpoint
+ * nilfs_tree_is_busy() - try to shrink dentries of a checkpoint
* @root_dentry: root dentry of the tree to be shrunk
*
* This function returns true if the tree was in-use.
*/
-static int nilfs_try_to_shrink_tree(struct dentry *root_dentry)
+static bool nilfs_tree_is_busy(struct dentry *root_dentry)
{
- if (have_submounts(root_dentry))
- return true;
shrink_dcache_parent(root_dentry);
- return nilfs_tree_was_touched(root_dentry);
+ return d_count(root_dentry) > 1;
}
int nilfs_checkpoint_is_mounted(struct super_block *sb, __u64 cno)
@@ -1034,8 +1027,7 @@ int nilfs_checkpoint_is_mounted(struct super_block *sb, __u64 cno)
if (inode) {
dentry = d_find_alias(inode);
if (dentry) {
- if (nilfs_tree_was_touched(dentry))
- ret = nilfs_try_to_shrink_tree(dentry);
+ ret = nilfs_tree_is_busy(dentry);
dput(dentry);
}
iput(inode);
@@ -1331,11 +1323,8 @@ nilfs_mount(struct file_system_type *fs_type, int flags,
s->s_flags |= MS_ACTIVE;
} else if (!sd.cno) {
- int busy = false;
-
- if (nilfs_tree_was_touched(s->s_root)) {
- busy = nilfs_try_to_shrink_tree(s->s_root);
- if (busy && (flags ^ s->s_flags) & MS_RDONLY) {
+ if (nilfs_tree_is_busy(s->s_root)) {
+ if ((flags ^ s->s_flags) & MS_RDONLY) {
printk(KERN_ERR "NILFS: the device already "
"has a %s mount.\n",
(s->s_flags & MS_RDONLY) ?
@@ -1343,8 +1332,7 @@ nilfs_mount(struct file_system_type *fs_type, int flags,
err = -EBUSY;
goto failed_super;
}
- }
- if (!busy) {
+ } else {
/*
* Try remount to setup mount states if the current
* tree is not mounted and only snapshots use this sb.
--
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