[PATCH] fs: pipe/sockets/anon dentries should have themselves asparent
From: Eric Dumazet
Date: Fri Nov 21 2008 - 12:59:48 EST
Christoph Hellwig a écrit :
On Fri, Nov 21, 2008 at 04:13:38PM +0100, Eric Dumazet wrote:
[PATCH] fs: pipe/sockets/anon dentries should not have a parent
Linking pipe/sockets/anon dentries to one root 'parent' has no functional
impact at all, but a scalability one.
We can avoid touching a cache line at allocation stage (inside d_alloc(), no need
to touch root->d_count), but also at freeing time (in d_kill, decrementing d_count)
We avoid an expensive atomic_dec_and_lock() call on the root dentry.
If we correct dnotify_parent() and inotify_d_instantiate() to take into account
a NULL d_parent, we can call d_alloc() with a NULL parent instead of root dentry.
Sorry folks, but a NULL d_parent is a no-go from the VFS perspective,
but you can set d_parent to the dentry itself which is the magic used
for root of tree dentries. They should also be marked
DCACHE_DISCONNECTED to make sure this is not unexpected.
And this kind of stuff really needs to go through -fsdevel.
Thanks Christoph for your review, sorry for fsdevel being forgotten.
d_alloc_root() is not an option here, since we also want such dentries
to be unhashed. So here is a second version, with the introduction
of a new helper, d_alloc_unhashed(), to be used by pipes, sockets and anon
I got even better numbers, probably because dnotify/inotify dont have
the NULL d_parent test anymore.
[PATCH] fs: pipe/sockets/anon dentries should have themselves as parent
Linking pipe/sockets/anon dentries to one root 'parent' has no functional
impact at all, but a scalability one.
We can avoid touching a cache line at allocation stage (inside d_alloc(), no need
to touch root->d_count), but also at freeing time (in d_kill, decrementing d_count)
We avoid an expensive atomic_dec_and_lock() call on the root dentry.
We add d_alloc_unhashed(const char *name, struct inode *inode) helper
to be used by pipes/socket/anon. This function is about the same as
d_alloc_root() but for unhashed entries.
Before patch, time to run 8 * 1 million of close(socket()) calls on 8 CPUS was :
real 0m27.496s
user 0m0.657s
sys 3m39.092s
After patch :
real 0m23.843s
user 0m0.616s
sys 3m9.732s
Old oprofile :
CPU: Core 2, speed 3000.11 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (Unhalted core cycles) count 100000
samples cum. samples % cum. % symbol name
164257 164257 11.0245 11.0245 init_file
155488 319745 10.4359 21.4604 d_alloc
151887 471632 10.1942 31.6547 _atomic_dec_and_lock
91620 563252 6.1493 37.8039 inet_create
74245 637497 4.9831 42.7871 kmem_cache_alloc
46702 684199 3.1345 45.9216 dentry_iput
46186 730385 3.0999 49.0215 tcp_close
42824 773209 2.8742 51.8957 kmem_cache_free
37275 810484 2.5018 54.3975 wake_up_inode
36553 847037 2.4533 56.8508 tcp_v4_init_sock
35661 882698 2.3935 59.2443 inotify_d_instantiate
32998 915696 2.2147 61.4590 sysenter_past_esp
31442 947138 2.1103 63.5693 d_instantiate
31303 978441 2.1010 65.6703 generic_forget_inode
27533 1005974 1.8479 67.5183 vfs_dq_drop
24237 1030211 1.6267 69.1450 sock_attach_fd
19290 1049501 1.2947 70.4397 __copy_from_user_ll
New oprofile :
CPU: Core 2, speed 3000.11 MHz (estimated)
Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (Unhalted core cycles) count 100000
samples cum. samples % cum. % symbol name
148703 148703 10.8581 10.8581 inet_create
116680 265383 8.5198 19.3779 new_inode
108912 374295 7.9526 27.3306 init_file
82911 457206 6.0541 33.3846 kmem_cache_alloc
65690 522896 4.7966 38.1812 wake_up_inode
53286 576182 3.8909 42.0721 _atomic_dec_and_lock
43814 619996 3.1992 45.2713 generic_forget_inode
41993 661989 3.0663 48.3376 d_alloc
41244 703233 3.0116 51.3492 kmem_cache_free
39244 742477 2.8655 54.2148 tcp_v4_init_sock
37402 779879 2.7310 56.9458 tcp_close
33336 813215 2.4342 59.3800 sysenter_past_esp
28596 841811 2.0880 61.4680 inode_has_buffers
25769 867580 1.8816 63.3496 d_kill
22606 890186 1.6507 65.0003 dentry_iput
20224 910410 1.4767 66.4770 vfs_dq_drop
19800 930210 1.4458 67.9228 __copy_from_user_ll
Signed-off-by: Eric Dumazet <dada1@xxxxxxxxxxxxx>
---
fs/anon_inodes.c | 9 +--------
fs/dcache.c | 31 +++++++++++++++++++++++++++++++
fs/pipe.c | 10 +---------
include/linux/dcache.h | 1 +
net/socket.c | 10 +---------
5 files changed, 35 insertions(+), 26 deletions(-)
diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 3662dd4..9fd0515 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -71,7 +71,6 @@ static struct dentry_operations anon_inodefs_dentry_operations = {
int anon_inode_getfd(const char *name, const struct file_operations *fops,
void *priv, int flags)
{
- struct qstr this;
struct dentry *dentry;
struct file *file;
int error, fd;
@@ -89,10 +88,7 @@ int anon_inode_getfd(const char *name, const struct file_operations *fops,
* using the inode sequence number.
*/
error = -ENOMEM;
- this.name = name;
- this.len = strlen(name);
- this.hash = 0;
- dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
+ dentry = d_alloc_unhashed(name, anon_inode_inode);
if (!dentry)
goto err_put_unused_fd;
@@ -104,9 +100,6 @@ int anon_inode_getfd(const char *name, const struct file_operations *fops,
atomic_inc(&anon_inode_inode->i_count);
dentry->d_op = &anon_inodefs_dentry_operations;
- /* Do not publish this dentry inside the global dentry hash table */
- dentry->d_flags &= ~DCACHE_UNHASHED;
- d_instantiate(dentry, anon_inode_inode);
error = -ENFILE;
file = alloc_file(anon_inode_mnt, dentry,
diff --git a/fs/dcache.c b/fs/dcache.c
index a1d86c7..a5477fd 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1111,6 +1111,37 @@ struct dentry * d_alloc_root(struct inode * root_inode)
return res;
}
+/**
+ * d_alloc_unhashed - allocate unhashed dentry
+ * @inode: inode to allocate the dentry for
+ * @name: dentry name
+ *
+ * Allocate an unhashed dentry for the inode given. The inode is
+ * instantiated and returned. %NULL is returned if there is insufficient
+ * memory. Unhashed dentries have themselves as a parent.
+ */
+
+struct dentry * d_alloc_unhashed(const char *name, struct inode *inode)
+{
+ struct qstr q = { .name = name, .len = strlen(name) };
+ struct dentry *res;
+
+ res = d_alloc(NULL, &q);
+ if (res) {
+ res->d_sb = inode->i_sb;
+ res->d_parent = res;
+ /*
+ * We dont want to push this dentry into global dentry hash table.
+ * We pretend dentry is already hashed, by unsetting DCACHE_UNHASHED
+ * This permits a working /proc/$pid/fd/XXX on sockets,pipes,anon
+ */
+ res->d_flags &= ~DCACHE_UNHASHED;
+ res->d_flags |= DCACHE_DISCONNECTED;
+ d_instantiate(res, inode);
+ }
+ return res;
+}
+
static inline struct hlist_head *d_hash(struct dentry *parent,
unsigned long hash)
{
diff --git a/fs/pipe.c b/fs/pipe.c
index 7aea8b8..29fcac2 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -918,7 +918,6 @@ struct file *create_write_pipe(int flags)
struct inode *inode;
struct file *f;
struct dentry *dentry;
- struct qstr name = { .name = "" };
err = -ENFILE;
inode = get_pipe_inode();
@@ -926,18 +925,11 @@ struct file *create_write_pipe(int flags)
goto err;
err = -ENOMEM;
- dentry = d_alloc(pipe_mnt->mnt_sb->s_root, &name);
+ dentry = d_alloc_unhashed("", inode);
if (!dentry)
goto err_inode;
dentry->d_op = &pipefs_dentry_operations;
- /*
- * We dont want to publish this dentry into global dentry hash table.
- * We pretend dentry is already hashed, by unsetting DCACHE_UNHASHED
- * This permits a working /proc/$pid/fd/XXX on pipes
- */
- dentry->d_flags &= ~DCACHE_UNHASHED;
- d_instantiate(dentry, inode);
err = -ENFILE;
f = alloc_file(pipe_mnt, dentry, FMODE_WRITE, &write_pipefifo_fops);
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index a37359d..12438d6 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -238,6 +238,7 @@ extern int d_invalidate(struct dentry *);
/* only used at mount-time */
extern struct dentry * d_alloc_root(struct inode *);
+extern struct dentry * d_alloc_unhashed(const char *, struct inode *);
/* <clickety>-<click> the ramfs-type tree */
extern void d_genocide(struct dentry *);
diff --git a/net/socket.c b/net/socket.c
index e9d65ea..b659b5d 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -371,20 +371,12 @@ static int sock_alloc_fd(struct file **filep, int flags)
static int sock_attach_fd(struct socket *sock, struct file *file, int flags)
{
struct dentry *dentry;
- struct qstr name = { .name = "" };
- dentry = d_alloc(sock_mnt->mnt_sb->s_root, &name);
+ dentry = d_alloc_unhashed("", SOCK_INODE(sock));
if (unlikely(!dentry))
return -ENOMEM;
dentry->d_op = &sockfs_dentry_operations;
- /*
- * We dont want to push this dentry into global dentry hash table.
- * We pretend dentry is already hashed, by unsetting DCACHE_UNHASHED
- * This permits a working /proc/$pid/fd/XXX on sockets
- */
- dentry->d_flags &= ~DCACHE_UNHASHED;
- d_instantiate(dentry, SOCK_INODE(sock));
sock->file = file;
init_file(file, sock_mnt, dentry, FMODE_READ | FMODE_WRITE,