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fs: fs_struct rwlock to spinlock

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fs: fs_struct rwlock to spinlock

struct fs_struct.lock is an rwlock with the read-side used to protect root and
pwd members while taking references to them. Taking a reference to a path
typically requires just 2 atomic ops, so the critical section is very small.
Parallel read-side operations would have cacheline contention on the lock, the
dentry, and the vfsmount cachelines, so the rwlock is unlikely to ever give a
real parallelism increase.

Replace it with a spinlock to avoid one or two atomic operations in typical
path lookup fastpath.

Signed-off-by: Nick Piggin <npiggin@kernel.dk>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Nick Piggin
2010-08-18 04:37:33 +10:00
committed by Al Viro
parent 44672e4fbd
commit 2a4419b5b2
5 changed files with 34 additions and 34 deletions
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14
include/linux/fs_struct.h
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@@ -5,7 +5,7 @@
struct fs_struct {
int users;
rwlock_t lock;
spinlock_t lock;
int umask;
int in_exec;
struct path root, pwd;
@@ -23,29 +23,29 @@ extern int unshare_fs_struct(void);
static inline void get_fs_root(struct fs_struct *fs, struct path *root)
{
read_lock(&fs->lock);
spin_lock(&fs->lock);
*root = fs->root;
path_get(root);
read_unlock(&fs->lock);
spin_unlock(&fs->lock);
}
static inline void get_fs_pwd(struct fs_struct *fs, struct path *pwd)
{
read_lock(&fs->lock);
spin_lock(&fs->lock);
*pwd = fs->pwd;
path_get(pwd);
read_unlock(&fs->lock);
spin_unlock(&fs->lock);
}
static inline void get_fs_root_and_pwd(struct fs_struct *fs, struct path *root,
struct path *pwd)
{
read_lock(&fs->lock);
spin_lock(&fs->lock);
*root = fs->root;
path_get(root);
*pwd = fs->pwd;
path_get(pwd);
read_unlock(&fs->lock);
spin_unlock(&fs->lock);
}
#endif /* _LINUX_FS_STRUCT_H */