diff options
| author | Nick Piggin <npiggin@kernel.dk> | 2010-08-18 04:37:33 +1000 |
|---|---|---|
| committer | Al Viro <viro@zeniv.linux.org.uk> | 2010-08-18 08:35:46 -0400 |
| commit | 2a4419b5b2a77f3f4537c14f7ad7df95770655dd (patch) | |
| tree | ad66519a92b995920ecada788e4a08e265747545 /kernel/fork.c | |
| parent | 44672e4fbd40e2dda8bbce7d0f71d24dbfc7e00e (diff) | |
| download | lwn-2a4419b5b2a77f3f4537c14f7ad7df95770655dd.tar.gz lwn-2a4419b5b2a77f3f4537c14f7ad7df95770655dd.zip | |
fs: fs_struct rwlock to spinlock
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>
Diffstat (limited to 'kernel/fork.c')
| -rw-r--r-- | kernel/fork.c | 10 |
1 files changed, 5 insertions, 5 deletions
diff --git a/kernel/fork.c b/kernel/fork.c index 98b450876f93..856eac3ec52e 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -752,13 +752,13 @@ static int copy_fs(unsigned long clone_flags, struct task_struct *tsk) struct fs_struct *fs = current->fs; if (clone_flags & CLONE_FS) { /* tsk->fs is already what we want */ - write_lock(&fs->lock); + spin_lock(&fs->lock); if (fs->in_exec) { - write_unlock(&fs->lock); + spin_unlock(&fs->lock); return -EAGAIN; } fs->users++; - write_unlock(&fs->lock); + spin_unlock(&fs->lock); return 0; } tsk->fs = copy_fs_struct(fs); @@ -1676,13 +1676,13 @@ SYSCALL_DEFINE1(unshare, unsigned long, unshare_flags) if (new_fs) { fs = current->fs; - write_lock(&fs->lock); + spin_lock(&fs->lock); current->fs = new_fs; if (--fs->users) new_fs = NULL; else new_fs = fs; - write_unlock(&fs->lock); + spin_unlock(&fs->lock); } if (new_mm) { |