From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Date: Fri, 22 Jul 2011 08:44:51 -0700
Subject: [PATCH 1/2] VFS: Cut down inode->i_op->xyz accesses in path walking
One of the biggest remaining unnecessary costs in path walking is the
pointer chasing in inode operations. We already avoided the
dentry->d_op derferences with the DCACHE_OP_xyz flags, this just starts
doing the same thing for the i_op->xyz cases.
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
fs/dcache.c | 6 ++++++
fs/namei.c | 25 +++++++++++++------------
include/linux/dcache.h | 12 +++++++++---
3 files changed, 28 insertions(+), 15 deletions(-)
diff --git a/fs/dcache.c b/fs/dcache.c
index fbdcbca40725..2dacddb7b101 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1374,6 +1374,12 @@ static void __d_instantiate(struct dentry *dentry, struct inode *inode)
if (unlikely(IS_AUTOMOUNT(inode)))
dentry->d_flags |= DCACHE_NEED_AUTOMOUNT;
list_add(&dentry->d_alias, &inode->i_dentry);
+ if (unlikely(inode->i_op->lookup))
+ dentry->d_flags |= DCACHE_OP_LOOKUP;
+ if (unlikely(inode->i_op->permission))
+ dentry->d_flags |= DCACHE_OP_PERMISSION;
+ if (unlikely(inode->i_op->follow_link))
+ dentry->d_flags |= DCACHE_OP_FOLLOW_LINK;
}
dentry->d_inode = inode;
dentry_rcuwalk_barrier(dentry);
diff --git a/fs/namei.c b/fs/namei.c
index 14ab8d3f2f0c..02b680e0e816 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -577,12 +577,12 @@ static int complete_walk(struct nameidata *nd)
* short-cut DAC fails, then call ->permission() to do more
* complete permission check.
*/
-static inline int exec_permission(struct inode *inode, unsigned int flags)
+static inline int exec_permission(struct dentry *dentry, struct inode *inode, unsigned int flags)
{
int ret;
struct user_namespace *ns = inode_userns(inode);
- if (inode->i_op->permission) {
+ if (dentry->d_flags & DCACHE_OP_PERMISSION) {
ret = inode->i_op->permission(inode, MAY_EXEC, flags);
} else {
ret = acl_permission_check(inode, MAY_EXEC, flags,
@@ -1234,13 +1234,13 @@ retry:
static inline int may_lookup(struct nameidata *nd)
{
if (nd->flags & LOOKUP_RCU) {
- int err = exec_permission(nd->inode, IPERM_FLAG_RCU);
+ int err = exec_permission(nd->path.dentry, nd->inode, IPERM_FLAG_RCU);
if (err != -ECHILD)
return err;
if (unlazy_walk(nd, NULL))
return -ECHILD;
}
- return exec_permission(nd->inode, 0);
+ return exec_permission(nd->path.dentry, nd->inode, 0);
}
static inline int handle_dots(struct nameidata *nd, int type)
@@ -1290,7 +1290,7 @@ static inline int walk_component(struct nameidata *nd, struct path *path,
terminate_walk(nd);
return -ENOENT;
}
- if (unlikely(inode->i_op->follow_link) && follow) {
+ if (unlikely(path->dentry->d_flags & DCACHE_OP_FOLLOW_LINK) && follow) {
if (nd->flags & LOOKUP_RCU) {
if (unlikely(unlazy_walk(nd, path->dentry))) {
terminate_walk(nd);
@@ -1425,7 +1425,7 @@ static int link_path_walk(const char *name, struct nameidata *nd)
return err;
}
err = -ENOTDIR;
- if (!nd->inode->i_op->lookup)
+ if (!(nd->path.dentry->d_flags & DCACHE_OP_LOOKUP))
break;
continue;
/* here ends the main loop */
@@ -1452,11 +1452,12 @@ static int path_init(int dfd, const char *name, unsigned int flags,
nd->flags = flags | LOOKUP_JUMPED;
nd->depth = 0;
if (flags & LOOKUP_ROOT) {
- struct inode *inode = nd->root.dentry->d_inode;
+ struct dentry *dentry = nd->root.dentry;
+ struct inode *inode = dentry->d_inode;
if (*name) {
- if (!inode->i_op->lookup)
+ if (!(dentry->d_flags & DCACHE_OP_LOOKUP))
return -ENOTDIR;
- retval = inode_permission(inode, MAY_EXEC);
+ retval = exec_permission(dentry, inode, 0);
if (retval)
return retval;
}
@@ -1599,7 +1600,7 @@ static int path_lookupat(int dfd, const char *name,
err = complete_walk(nd);
if (!err && nd->flags & LOOKUP_DIRECTORY) {
- if (!nd->inode->i_op->lookup) {
+ if (!(nd->path.dentry->d_flags & DCACHE_OP_LOOKUP)) {
path_put(&nd->path);
err = -ENOTDIR;
}
@@ -1672,7 +1673,7 @@ static struct dentry *__lookup_hash(struct qstr *name,
struct dentry *dentry;
int err;
- err = exec_permission(inode, 0);
+ err = exec_permission(base, inode, 0);
if (err)
return ERR_PTR(err);
@@ -2099,7 +2100,7 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
error = -ENOTDIR;
if (nd->flags & LOOKUP_DIRECTORY) {
- if (!nd->inode->i_op->lookup)
+ if (!(nd->path.dentry->d_flags & DCACHE_OP_LOOKUP))
goto exit;
}
audit_inode(pathname, nd->path.dentry);
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 19d90a55541d..8cd1a3d5b320 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -208,14 +208,20 @@ struct dentry_operations {
#define DCACHE_CANT_MOUNT 0x0100
#define DCACHE_GENOCIDE 0x0200
+/* Avoid 'dentry->d_op->op' dereference chain */
#define DCACHE_OP_HASH 0x1000
#define DCACHE_OP_COMPARE 0x2000
#define DCACHE_OP_REVALIDATE 0x4000
#define DCACHE_OP_DELETE 0x8000
-#define DCACHE_MOUNTED 0x10000 /* is a mountpoint */
-#define DCACHE_NEED_AUTOMOUNT 0x20000 /* handle automount on this dir */
-#define DCACHE_MANAGE_TRANSIT 0x40000 /* manage transit from this dirent */
+/* Avoid 'inode->i_op->op' dereference chain */
+#define DCACHE_OP_LOOKUP 0x10000
+#define DCACHE_OP_PERMISSION 0x20000
+#define DCACHE_OP_FOLLOW_LINK 0x40000
+
+#define DCACHE_MOUNTED 0x100000 /* is a mountpoint */
+#define DCACHE_NEED_AUTOMOUNT 0x200000 /* handle automount on this dir */
+#define DCACHE_MANAGE_TRANSIT 0x400000 /* manage transit from this dirent */
#define DCACHE_MANAGED_DENTRY \
(DCACHE_MOUNTED|DCACHE_NEED_AUTOMOUNT|DCACHE_MANAGE_TRANSIT)
--
1.7.6.233.gd79bc.dirty
--
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