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Subject[PATCH 5/6] fs: Introduce special inodes
Goal of this patch is to not touch inode_lock for socket/pipes/anonfd
inodes allocation/freeing.

In new_inode(), we test if super block has MS_SPECIAL flag set.
If yes, we dont put inode in "inode_in_use" list nor "sb->s_inodes" list
As inode_lock was taken only to protect these lists, we avoid it as well

Using iput_special() from dput_special() avoids taking inode_lock
at freeing time.

This patch has a very noticeable effect, because we avoid dirtying
of three contended cache lines in new_inode(), and five cache lines
in iput()

Note: Not sure if we can use MS_SPECIAL=MS_NOUSER, or if we
really need a different flag.

(socket8 bench result : from 20.5s to 2.94s)

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
---
fs/anon_inodes.c | 1 +
fs/dcache.c | 2 +-
fs/inode.c | 25 ++++++++++++++++++-------
fs/pipe.c | 3 ++-
include/linux/fs.h | 2 ++
net/socket.c | 1 +
6 files changed, 25 insertions(+), 9 deletions(-)diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 4f20d48..a0212b3 100644
--- a/fs/anon_inodes.c
+++ b/fs/anon_inodes.c
@@ -158,6 +158,7 @@ static int __init anon_inode_init(void)
error = PTR_ERR(anon_inode_mnt);
goto err_unregister_filesystem;
}
+ anon_inode_mnt->mnt_sb->s_flags |= MS_SPECIAL;
anon_inode_inode = anon_inode_mkinode();
if (IS_ERR(anon_inode_inode)) {
error = PTR_ERR(anon_inode_inode);
diff --git a/fs/dcache.c b/fs/dcache.c
index d73763b..bade7d7 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -239,7 +239,7 @@ static void dput_special(struct dentry *dentry)
return;
inode = dentry->d_inode;
if (inode)
- iput(inode);
+ iput_special(inode);
d_free(dentry);
}

diff --git a/fs/inode.c b/fs/inode.c
index 8d8d40e..1bb6553 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -228,6 +228,14 @@ void destroy_inode(struct inode *inode)
kmem_cache_free(inode_cachep, (inode));
}

+void iput_special(struct inode *inode)
+{
+ if (atomic_dec_and_test(&inode->i_count)) {
+ destroy_inode(inode);
+ get_cpu_var(nr_inodes)--;
+ put_cpu_var(nr_inodes);
+ }
+}

/*
* These are initializations that only need to be done
@@ -609,18 +617,21 @@ struct inode *new_inode(struct super_block *sb)
*/
struct inode * inode;

- spin_lock_prefetch(&inode_lock);
-
inode = alloc_inode(sb);
if (inode) {
- spin_lock(&inode_lock);
- list_add(&inode->i_list, &inode_in_use);
- list_add(&inode->i_sb_list, &sb->s_inodes);
+ inode->i_state = 0;
+ if (sb->s_flags & MS_SPECIAL) {
+ INIT_LIST_HEAD(&inode->i_list);
+ INIT_LIST_HEAD(&inode->i_sb_list);
+ } else {
+ spin_lock(&inode_lock);
+ list_add(&inode->i_list, &inode_in_use);
+ list_add(&inode->i_sb_list, &sb->s_inodes);
+ spin_unlock(&inode_lock);
+ }
get_cpu_var(nr_inodes)--;
inode->i_ino = last_ino_get();
put_cpu_var(nr_inodes);
- inode->i_state = 0;
- spin_unlock(&inode_lock);
}
return inode;
}
diff --git a/fs/pipe.c b/fs/pipe.c
index 5cc132a..6fca681 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1078,7 +1078,8 @@ static int __init init_pipe_fs(void)
if (IS_ERR(pipe_mnt)) {
err = PTR_ERR(pipe_mnt);
unregister_filesystem(&pipe_fs_type);
- }
+ } else
+ pipe_mnt->mnt_sb->s_flags |= MS_SPECIAL;
}
return err;
}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 2482977..dd0e8a5 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -136,6 +136,7 @@ extern int dir_notify_enable;
#define MS_RELATIME (1<<21) /* Update atime relative to mtime/ctime. */
#define MS_KERNMOUNT (1<<22) /* this is a kern_mount call */
#define MS_I_VERSION (1<<23) /* Update inode I_version field */
+#define MS_SPECIAL (1<<24) /* special fs (inodes not in sb->s_inodes) */
#define MS_ACTIVE (1<<30)
#define MS_NOUSER (1<<31)

@@ -1898,6 +1899,7 @@ extern void __iget(struct inode * inode);
extern void iget_failed(struct inode *);
extern void clear_inode(struct inode *);
extern void destroy_inode(struct inode *);
+extern void iput_special(struct inode *inode);
extern struct inode *new_inode(struct super_block *);
extern int should_remove_suid(struct dentry *);
extern int file_remove_suid(struct file *);
diff --git a/net/socket.c b/net/socket.c
index f41b6c6..4177456 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2205,6 +2205,7 @@ static int __init sock_init(void)
init_inodecache();
register_filesystem(&sock_fs_type);
sock_mnt = kern_mount(&sock_fs_type);
+ sock_mnt->mnt_sb->s_flags |= MS_SPECIAL;

/* The real protocol initialization is performed in later initcalls.
*/
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