[PATCH] dentry shrinkage

Rework dentries so that the inline name length is between 31 and 48 bytes.

On SMP P4-compiled x86 each dentry consumes 160 bytes (24 per page).

Here's the histogram of name lengths on all 1.5M files on my workstation:

1:  0%
2:  0%
3:  1%
4:  5%
5:  8%
6:  13%
7:  19%
8:  26%
9:  33%
10:  42%
11:  49%
12:  55%
13:  60%
14:  64%
15:  67%
16:  69%
17:  71%
18:  73%
19:  75%
20:  76%
21:  78%
22:  79%
23:  80%
24:  81%
25:  82%
26:  83%
27:  85%
28:  86%
29:  87%
30:  88%
31:  89%
32:  90%
33:  91%
34:  92%
35:  93%
36:  94%
37:  95%
38:  96%
39:  96%
40:  96%
41:  96%
42:  96%
43:  96%
44:  97%
45:  97%
46:  97%
47:  97%
48:  97%
49:  98%
50:  98%
51:  98%
52:  98%
53:  98%
54:  98%
55:  98%
56:  98%
57:  98%
58:  98%
59:  98%
60:  99%
61:  99%
62:  99%
63:  99%
64:  99%

So on x86 we'll fit 89% of filenames into the inline name.


The patch also removes the NAME_ALLOC_LEN() rounding-up of the storage for the
out-of-line names.  That seems unnecessary.

1 files changed, 1 insertions, 5 deletions

diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 74f22a171e19..7b612005423b 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -74,8 +74,6 @@ full_name_hash(const unsigned char *name, unsigned int len)
 	return end_name_hash(hash);
 }
 
-#define DNAME_INLINE_LEN_MIN 24
-
 struct dcookie_struct;
  
 struct dentry {
@@ -101,11 +99,9 @@ struct dentry {
 	struct qstr d_name;
 	struct hlist_node d_hash;	/* lookup hash list */	
 	struct hlist_head * d_bucket;	/* lookup hash bucket */
-	unsigned char d_iname[DNAME_INLINE_LEN_MIN]; /* small names */
+	unsigned char d_iname[0];	/* small names */
 };
 
-#define DNAME_INLINE_LEN	(sizeof(struct dentry)-offsetof(struct dentry,d_iname))
- 
 struct dentry_operations {
 	int (*d_revalidate)(struct dentry *, struct nameidata *);
 	int (*d_hash) (struct dentry *, struct qstr *);