Some fs are hardwired into kernel, and mntput()/mntget() hit a contended
cache line. We define a new superblock flag, MS_NOREFCOUNT, that is set
on socket, pipes and anonymous fd superblocks. mntput()/mntget() become
null ops on these fs.
("socketallocbench -n 8" result : from 2.20s to 1.64s)
Signed-off-by: Eric Dumazet <dada1@xxxxxxxxxxxxx>
---
fs/anon_inodes.c | 1 +
fs/pipe.c | 3 ++-
include/linux/fs.h | 2 ++
include/linux/mount.h | 8 +++-----
net/socket.c | 1 +
5 files changed, 9 insertions(+), 6 deletions(-)
diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c
index 89fd36d..de0ec3b 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_NOREFCOUNT;
anon_inode_inode = anon_inode_mkinode();
if (IS_ERR(anon_inode_inode)) {
error = PTR_ERR(anon_inode_inode);
diff --git a/fs/pipe.c b/fs/pipe.c
index 8c51a0d..f547432 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_NOREFCOUNT;
}
return err;
}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index a1f56d4..11b0452 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -137,6 +137,8 @@ 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_NOREFCOUNT (1<<29) /* kernel static mnt : no refcounting needed */
#define MS_ACTIVE (1<<30)
#define MS_NOUSER (1<<31)
diff --git a/include/linux/mount.h b/include/linux/mount.h
index cab2a85..51418b5 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -14,10 +14,8 @@
#include <linux/nodemask.h>
#include <linux/spinlock.h>
#include <asm/atomic.h>
+#include <linux/fs.h>
-struct super_block;
-struct vfsmount;
-struct dentry;
struct mnt_namespace;
#define MNT_NOSUID 0x01
@@ -73,7 +71,7 @@ struct vfsmount {
static inline struct vfsmount *mntget(struct vfsmount *mnt)
{
- if (mnt)
+ if (mnt && !(mnt->mnt_sb->s_flags & MS_NOREFCOUNT))
atomic_inc(&mnt->mnt_count);
return mnt;
}
@@ -87,7 +85,7 @@ extern int __mnt_is_readonly(struct vfsmount *mnt);
static inline void mntput(struct vfsmount *mnt)
{
- if (mnt) {
+ if (mnt && !(mnt->mnt_sb->s_flags & MS_NOREFCOUNT)) {
mnt->mnt_expiry_mark = 0;
mntput_no_expire(mnt);
}
diff --git a/net/socket.c b/net/socket.c
index 4017409..2534dbc 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2206,6 +2206,7 @@ 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_NOREFCOUNT;
/* The real protocol initialization is performed in later initcalls.
*/
--
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