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SubjectRe: dentry bloat.
Andrew Morton <akpm@osdl.org> wrote:
>
> Here be another patch.


Can't help myself!


- d_vfs_flags can be removed - just use d_flags. It looks like someone
added d_vfs_flags with the intent of doing bitops on it, but all
modifications are under dcache_lock. 4 bytes saved.

- make d_flags a ushort.

- Assume that nobody wants filenames longer than 64k and make qstr.len
unsigned short too.

- Pack things so that dentry.d_name.len and dentry.d_flags occupy the same
word. 4 bytes saved.

- NFS and AFS are modifying d_flags without dcache_lock.


On x86 this takes the internal string size up to 44 bytes. The
internal/external ratio on my 1.5M files hits 96%.



---

25-akpm/fs/dcache.c | 17 ++++++++---------
25-akpm/include/linux/dcache.h | 33 +++++++++++++++++----------------
2 files changed, 25 insertions(+), 25 deletions(-)

diff -puN include/linux/dcache.h~dentry-more-shrinkage include/linux/dcache.h
--- 25/include/linux/dcache.h~dentry-more-shrinkage 2004-05-08 02:46:53.134693712 -0700
+++ 25-akpm/include/linux/dcache.h 2004-05-08 02:56:16.687020736 -0700
@@ -30,9 +30,9 @@ struct vfsmount;
*/
struct qstr {
const unsigned char *name;
- unsigned int len;
unsigned int hash;
-};
+ unsigned short len;
+} __attribute__((packed));

struct dentry_stat_t {
int nr_dentry;
@@ -77,28 +77,29 @@ struct dcookie_struct;

struct dentry {
atomic_t d_count;
- unsigned long d_vfs_flags; /* moved here to be on same cacheline */
spinlock_t d_lock; /* per dentry lock */
- struct inode * d_inode; /* Where the name belongs to - NULL is negative */
+ struct inode *d_inode; /* Where the name belongs to - NULL is
+ * negative */
struct list_head d_lru; /* LRU list */
struct list_head d_child; /* child of parent list */
struct list_head d_subdirs; /* our children */
struct list_head d_alias; /* inode alias list */
unsigned long d_time; /* used by d_revalidate */
- struct dentry_operations *d_op;
- struct super_block * d_sb; /* The root of the dentry tree */
- unsigned int d_flags;
+ struct dentry_operations *d_op;
+ struct super_block *d_sb; /* The root of the dentry tree */
int d_mounted;
- void * d_fsdata; /* fs-specific data */
+ void *d_fsdata; /* fs-specific data */
struct rcu_head d_rcu;
- struct dcookie_struct * d_cookie; /* cookie, if any */
- unsigned long d_move_count; /* to indicated moved dentry while lockless lookup */
- struct dentry * d_parent; /* parent directory */
+ struct dcookie_struct *d_cookie; /* cookie, if any */
+ unsigned long d_move_count; /* to indicated moved dentry while
+ * lockless lookup */
+ struct dentry *d_parent; /* parent directory */
struct qstr d_name;
+ unsigned short d_flags;
struct hlist_node d_hash; /* lookup hash list */
- struct hlist_head * d_bucket; /* lookup hash bucket */
+ struct hlist_head *d_bucket; /* lookup hash bucket */
unsigned char d_iname[0]; /* small names */
-};
+} __attribute__((packed));

struct dentry_operations {
int (*d_revalidate)(struct dentry *, struct nameidata *);
@@ -169,8 +170,8 @@ extern spinlock_t dcache_lock;

static inline void __d_drop(struct dentry *dentry)
{
- if (!(dentry->d_vfs_flags & DCACHE_UNHASHED)) {
- dentry->d_vfs_flags |= DCACHE_UNHASHED;
+ if (!(dentry->d_flags & DCACHE_UNHASHED)) {
+ dentry->d_flags |= DCACHE_UNHASHED;
hlist_del_rcu(&dentry->d_hash);
}
}
@@ -281,7 +282,7 @@ extern struct dentry * dget_locked(struc

static inline int d_unhashed(struct dentry *dentry)
{
- return (dentry->d_vfs_flags & DCACHE_UNHASHED);
+ return (dentry->d_flags & DCACHE_UNHASHED);
}

static inline struct dentry *dget_parent(struct dentry *dentry)
diff -puN fs/dcache.c~dentry-more-shrinkage fs/dcache.c
--- 25/fs/dcache.c~dentry-more-shrinkage 2004-05-08 02:55:55.284274448 -0700
+++ 25-akpm/fs/dcache.c 2004-05-08 02:57:10.581827480 -0700
@@ -168,7 +168,7 @@ repeat:
if (d_unhashed(dentry))
goto kill_it;
if (list_empty(&dentry->d_lru)) {
- dentry->d_vfs_flags |= DCACHE_REFERENCED;
+ dentry->d_flags |= DCACHE_REFERENCED;
list_add(&dentry->d_lru, &dentry_unused);
dentry_stat.nr_unused++;
}
@@ -401,8 +401,8 @@ static void prune_dcache(int count)
continue;
}
/* If the dentry was recently referenced, don't free it. */
- if (dentry->d_vfs_flags & DCACHE_REFERENCED) {
- dentry->d_vfs_flags &= ~DCACHE_REFERENCED;
+ if (dentry->d_flags & DCACHE_REFERENCED) {
+ dentry->d_flags &= ~DCACHE_REFERENCED;
list_add(&dentry->d_lru, &dentry_unused);
dentry_stat.nr_unused++;
spin_unlock(&dentry->d_lock);
@@ -707,9 +707,8 @@ struct dentry *d_alloc(struct dentry * p
dname[name->len] = 0;

atomic_set(&dentry->d_count, 1);
- dentry->d_vfs_flags = DCACHE_UNHASHED;
+ dentry->d_flags = DCACHE_UNHASHED;
dentry->d_lock = SPIN_LOCK_UNLOCKED;
- dentry->d_flags = 0;
dentry->d_inode = NULL;
dentry->d_parent = NULL;
dentry->d_move_count = 0;
@@ -855,7 +854,7 @@ struct dentry * d_alloc_anon(struct inod
res->d_inode = inode;
res->d_bucket = d_hash(res, res->d_name.hash);
res->d_flags |= DCACHE_DISCONNECTED;
- res->d_vfs_flags &= ~DCACHE_UNHASHED;
+ res->d_flags &= ~DCACHE_UNHASHED;
list_add(&res->d_alias, &inode->i_dentry);
hlist_add_head(&res->d_hash, &inode->i_sb->s_anon);
spin_unlock(&res->d_lock);
@@ -1117,7 +1116,7 @@ void d_rehash(struct dentry * entry)
{
struct hlist_head *list = d_hash(entry->d_parent, entry->d_name.hash);
spin_lock(&dcache_lock);
- entry->d_vfs_flags &= ~DCACHE_UNHASHED;
+ entry->d_flags &= ~DCACHE_UNHASHED;
entry->d_bucket = list;
hlist_add_head_rcu(&entry->d_hash, list);
spin_unlock(&dcache_lock);
@@ -1214,14 +1213,14 @@ void d_move(struct dentry * dentry, stru
}

/* Move the dentry to the target hash queue, if on different bucket */
- if (dentry->d_vfs_flags & DCACHE_UNHASHED)
+ if (dentry->d_flags & DCACHE_UNHASHED)
goto already_unhashed;
if (dentry->d_bucket != target->d_bucket) {
hlist_del_rcu(&dentry->d_hash);
already_unhashed:
dentry->d_bucket = target->d_bucket;
hlist_add_head_rcu(&dentry->d_hash, target->d_bucket);
- dentry->d_vfs_flags &= ~DCACHE_UNHASHED;
+ dentry->d_flags &= ~DCACHE_UNHASHED;
}

/* Unhash the target: dput() will then get rid of it */
_

-
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