From: Hugh Dickins <hugh@veritas.com>
A tmpfs user reported increasingly slow directory reads when repeatedly
creating and unlinking in a mkstemp-like way. The negative dentries
accumulate alarmingly (until memory pressure finally frees them), and are
just a hindrance to any in-memory filesystem. simple_lookup set d_op to
arrange for negative dentries to be deleted immediately.
(But I failed to discover how it is that on-disk filesystems seem to keep
their negative dentries within manageable bounds: this effect was gross
with tmpfs or ramfs, but no problem at all with extN or reiser.)
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/fs/libfs.c | 17 +++++++++++++++--
1 files changed, 15 insertions(+), 2 deletions(-)
diff -puN fs/libfs.c~simple-fs-stop-ve-dentries fs/libfs.c
--- 25/fs/libfs.c~simple-fs-stop-ve-dentries Fri Aug 6 15:20:11 2004
+++ 25-akpm/fs/libfs.c Fri Aug 6 15:20:11 2004
@@ -27,14 +27,27 @@ int simple_statfs(struct super_block *sb
}
/*
- * Lookup the data. This is trivial - if the dentry didn't already
- * exist, we know it is negative.
+ * Retaining negative dentries for an in-memory filesystem just wastes
+ * memory and lookup time: arrange for them to be deleted immediately.
*/
+static int simple_delete_dentry(struct dentry *dentry)
+{
+ return 1;
+}
+/*
+ * Lookup the data. This is trivial - if the dentry didn't already
+ * exist, we know it is negative. Set d_op to delete negative dentries.
+ */
struct dentry *simple_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
{
+ static struct dentry_operations simple_dentry_operations = {
+ .d_delete = simple_delete_dentry,
+ };
+
if (dentry->d_name.len > NAME_MAX)
return ERR_PTR(-ENAMETOOLONG);
+ dentry->d_op = &simple_dentry_operations;
d_add(dentry, NULL);
return NULL;
}
_