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.
Regards,
Ryusuke Konishi
--
From: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxxxxxx>
Date: Thu, 22 Aug 2013 01:53:03 +0900
Subject: [PATCH] nilfs2: do not use have_submounts()
The pre-check with have_submounts() in
nilfs_try_to_shrink_tree(root_dentry) is eliminable since the return
value of the function does not depend on whether the root_dentry has
sub-mounts or not. Removing the have_submount() pre-check may cause
unnecessary dcache shrinking, but the impact looks limited because
nilfs_try_to_shrink_tree() is not called in usual operation.
So, we remove use of have_submounts() from nilfs.
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxxxxxx>
---
fs/nilfs2/super.c | 2 --
1 file changed, 2 deletions(-)
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index af3ba04..38fe240 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -1007,8 +1007,6 @@ static int nilfs_tree_was_touched(struct dentry *root_dentry)
*/
static int nilfs_try_to_shrink_tree(struct dentry *root_dentry)
{
- if (have_submounts(root_dentry))
- return true;
shrink_dcache_parent(root_dentry);
return nilfs_tree_was_touched(root_dentry);
}
--
1.7.9.3
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