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Subject[patch 11/14] fs: dcache reduce dput locking
It is possible to run dput without taking locks up-front. In many cases
where we don't kill the dentry anyway, these locks are not required.

(I think... need to think about it more). Further changes ->d_delete
locking which is not all audited.

---
fs/dcache.c | 56 ++++++++++++++++++++++++++++++--------------------------
1 file changed, 30 insertions(+), 26 deletions(-)

Index: linux-2.6/fs/dcache.c
===================================================================
--- linux-2.6.orig/fs/dcache.c
+++ linux-2.6/fs/dcache.c
@@ -262,6 +262,7 @@ static struct dentry *d_kill(struct dent
void dput(struct dentry *dentry)
{
struct dentry *parent;
+
if (!dentry)
return;

@@ -269,23 +270,8 @@ repeat:
if (dentry->d_count == 1)
might_sleep();
spin_lock(&dentry->d_lock);
- if (dentry->d_count == 1) {
- if (!spin_trylock(&dcache_inode_lock)) {
-drop2:
- spin_unlock(&dentry->d_lock);
- goto repeat;
- }
- parent = dentry->d_parent;
- if (parent) {
- BUG_ON(parent == dentry);
- if (!spin_trylock(&parent->d_lock)) {
- spin_unlock(&dcache_inode_lock);
- goto drop2;
- }
- }
- }
- dentry->d_count--;
- if (dentry->d_count) {
+ if (dentry->d_count > 1) {
+ dentry->d_count--;
spin_unlock(&dentry->d_lock);
return;
}
@@ -294,8 +280,10 @@ drop2:
* AV: ->d_delete() is _NOT_ allowed to block now.
*/
if (dentry->d_op && dentry->d_op->d_delete) {
- if (dentry->d_op->d_delete(dentry))
- goto unhash_it;
+ if (dentry->d_op->d_delete(dentry)) {
+ __d_drop(dentry);
+ goto kill_it;
+ }
}
/* Unreachable? Get rid of it */
if (d_unhashed(dentry))
@@ -304,15 +292,31 @@ drop2:
dentry->d_flags |= DCACHE_REFERENCED;
dentry_lru_add(dentry);
}
- spin_unlock(&dentry->d_lock);
- if (parent)
- spin_unlock(&parent->d_lock);
- spin_unlock(&dcache_inode_lock);
- return;
+ dentry->d_count--;
+ spin_unlock(&dentry->d_lock);
+ return;

-unhash_it:
- __d_drop(dentry);
kill_it:
+ spin_unlock(&dentry->d_lock);
+ spin_lock(&dcache_inode_lock);
+relock:
+ spin_lock(&dentry->d_lock);
+ parent = dentry->d_parent;
+ if (parent) {
+ BUG_ON(parent == dentry);
+ if (!spin_trylock(&parent->d_lock)) {
+ spin_unlock(&dentry->d_lock);
+ goto relock;
+ }
+ }
+ dentry->d_count--;
+ if (dentry->d_count) {
+ spin_unlock(&dentry->d_lock);
+ spin_unlock(&parent->d_lock);
+ spin_unlock(&dcache_inode_lock);
+ printk("elevated d_count\n");
+ return;
+ }
/* if dentry was on the d_lru list delete it from there */
dentry_lru_del(dentry);
dentry = d_kill(dentry);



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