From 5160ee6fc891a9ca114be0e90fa6655647bb64b2 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Sun, 8 Jan 2006 01:03:32 -0800 Subject: [PATCH] shrink dentry struct Some long time ago, dentry struct was carefully tuned so that on 32 bits UP, sizeof(struct dentry) was exactly 128, ie a power of 2, and a multiple of memory cache lines. Then RCU was added and dentry struct enlarged by two pointers, with nice results for SMP, but not so good on UP, because breaking the above tuning (128 + 8 = 136 bytes) This patch reverts this unwanted side effect, by using an union (d_u), where d_rcu and d_child are placed so that these two fields can share their memory needs. At the time d_free() is called (and d_rcu is really used), d_child is known to be empty and not touched by the dentry freeing. Lockless lookups only access d_name, d_parent, d_lock, d_op, d_flags (so the previous content of d_child is not needed if said dentry was unhashed but still accessed by a CPU because of RCU constraints) As dentry cache easily contains millions of entries, a size reduction is worth the extra complexity of the ugly C union. Signed-off-by: Eric Dumazet Cc: Dipankar Sarma Cc: Maneesh Soni Cc: Miklos Szeredi Cc: "Paul E. McKenney" Cc: Ian Kent Cc: Paul Jackson Cc: Al Viro Cc: Christoph Hellwig Cc: Trond Myklebust Cc: Neil Brown Cc: James Morris Cc: Stephen Smalley Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/libfs.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) (limited to 'fs/libfs.c') diff --git a/fs/libfs.c b/fs/libfs.c index 58101dff2c66..9c50523382e7 100644 --- a/fs/libfs.c +++ b/fs/libfs.c @@ -93,16 +93,16 @@ loff_t dcache_dir_lseek(struct file *file, loff_t offset, int origin) loff_t n = file->f_pos - 2; spin_lock(&dcache_lock); - list_del(&cursor->d_child); + list_del(&cursor->d_u.d_child); p = file->f_dentry->d_subdirs.next; while (n && p != &file->f_dentry->d_subdirs) { struct dentry *next; - next = list_entry(p, struct dentry, d_child); + next = list_entry(p, struct dentry, d_u.d_child); if (!d_unhashed(next) && next->d_inode) n--; p = p->next; } - list_add_tail(&cursor->d_child, p); + list_add_tail(&cursor->d_u.d_child, p); spin_unlock(&dcache_lock); } } @@ -126,7 +126,7 @@ int dcache_readdir(struct file * filp, void * dirent, filldir_t filldir) { struct dentry *dentry = filp->f_dentry; struct dentry *cursor = filp->private_data; - struct list_head *p, *q = &cursor->d_child; + struct list_head *p, *q = &cursor->d_u.d_child; ino_t ino; int i = filp->f_pos; @@ -153,7 +153,7 @@ int dcache_readdir(struct file * filp, void * dirent, filldir_t filldir) } for (p=q->next; p != &dentry->d_subdirs; p=p->next) { struct dentry *next; - next = list_entry(p, struct dentry, d_child); + next = list_entry(p, struct dentry, d_u.d_child); if (d_unhashed(next) || !next->d_inode) continue; @@ -261,7 +261,7 @@ int simple_empty(struct dentry *dentry) int ret = 0; spin_lock(&dcache_lock); - list_for_each_entry(child, &dentry->d_subdirs, d_child) + list_for_each_entry(child, &dentry->d_subdirs, d_u.d_child) if (simple_positive(child)) goto out; ret = 1; -- cgit v1.2.3