[patch 18/52] fs: dcache reduce dput locking

npiggin
2010-06-24T03:16:22Z

[-- Attachment #1: dcache-dput-less-dcache_lock.patch --]
[-- Type: text/plain, Size: 2798 bytes --]

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. d_delete must be idempotent, for one.

Signed-off-by: Nick Piggin <npiggin@suse.de>
---
fs/dcache.c | 60 ++++++++++++++++++++++++++++++++----------------------------
1 file changed, 32 insertions(+), 28 deletions(-)

Index: linux-2.6/fs/dcache.c
===================================================================
--- linux-2.6.orig/fs/dcache.c
+++ linux-2.6/fs/dcache.c
@@ -278,7 +278,8 @@ static struct dentry *d_kill(struct dent

void dput(struct dentry *dentry)
{
- struct dentry *parent = NULL;
+ struct dentry *parent;
+
if (!dentry)
return;

@@ -286,25 +287,10 @@ 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 && parent != dentry) {
- if (!spin_trylock(&parent->d_lock)) {
- spin_unlock(&dcache_inode_lock);
- goto drop2;
- }
- }
- }
- dentry->d_count--;
- if (dentry->d_count) {
+ BUG_ON(!dentry->d_count);
+ if (dentry->d_count > 1) {
+ dentry->d_count--;
spin_unlock(&dentry->d_lock);
- if (parent && parent != dentry)
- spin_unlock(&parent->d_lock);
return;
}

@@ -312,8 +298,10 @@ 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))
@@ -322,15 +310,31 @@ drop2:
dentry->d_flags |= DCACHE_REFERENCED;
dentry_lru_add(dentry);
}
- spin_unlock(&dentry->d_lock);
- if (parent && parent != dentry)
- 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 && parent != dentry) {
+ if (!spin_trylock(&parent->d_lock)) {
+ spin_unlock(&dentry->d_lock);
+ goto relock;
+ }
+ }
+ dentry->d_count--;
+ if (dentry->d_count) {
+ /* This case should be fine */
+ spin_unlock(&dentry->d_lock);
+ if (parent && parent != dentry)
+ spin_unlock(&parent->d_lock);
+ spin_unlock(&dcache_inode_lock);
+ return;
+ }
/* if dentry was on the d_lru list delete it from there */
dentry_lru_del(dentry);
dentry = d_kill(dentry);