On Wed, 21 Aug 2013 22:00:38 +0100, Al Viro wrote:
> 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?
>
I confirmed the pre-check is also eliminable.
Then, yes, the following change is ok.
Reviewed-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxxxxxx>
Regards,
Ryusuke Konishi
> 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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