Improve scalability of mntget/mntput by using per-cpu counters protected by the reader side of the brlock vfsmount_lock. mnt_mounted keeps track of whether the vfsmount is actually attached to the tree so we can shortcut expensive checks in mntput. --- fs/libfs.c | 1 fs/namespace.c | 122 +++++++++++++++++++++++++++++++++++++++++++------- fs/pnode.c | 2 include/linux/mount.h | 33 ++++--------- 4 files changed, 121 insertions(+), 37 deletions(-) Index: linux-2.6/fs/namespace.c =================================================================== --- linux-2.6.orig/fs/namespace.c +++ linux-2.6/fs/namespace.c @@ -177,6 +177,49 @@ void mnt_release_group_id(struct vfsmoun mnt->mnt_group_id = 0; } +static inline void add_mnt_count(struct vfsmount *mnt, int n) +{ +#ifdef CONFIG_SMP + (*per_cpu_ptr(mnt->mnt_count, smp_processor_id())) += n; +#else + mnt->mnt_count += n; +#endif +} + +static inline void inc_mnt_count(struct vfsmount *mnt) +{ +#ifdef CONFIG_SMP + (*per_cpu_ptr(mnt->mnt_count, smp_processor_id()))++; +#else + mnt->mnt_count++; +#endif +} + +static inline void dec_mnt_count(struct vfsmount *mnt) +{ +#ifdef CONFIG_SMP + (*per_cpu_ptr(mnt->mnt_count, smp_processor_id()))--; +#else + mnt->mnt_count--; +#endif +} + +unsigned int count_mnt_count(struct vfsmount *mnt) +{ +#ifdef CONFIG_SMP + unsigned int count = 0; + int cpu; + + for_each_possible_cpu(cpu) { + count += *per_cpu_ptr(mnt->mnt_count, cpu); + } + + return count; +#else + return mnt->mnt_count; +#endif +} + struct vfsmount *alloc_vfsmnt(const char *name) { struct vfsmount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL); @@ -193,7 +236,13 @@ struct vfsmount *alloc_vfsmnt(const char goto out_free_id; } - atomic_set(&mnt->mnt_count, 1); +#ifdef CONFIG_SMP + mnt->mnt_count = alloc_percpu(int); + if (!mnt->mnt_count) + goto out_free_devname; +#else + mnt->mnt_count = 0; +#endif INIT_LIST_HEAD(&mnt->mnt_hash); INIT_LIST_HEAD(&mnt->mnt_child); INIT_LIST_HEAD(&mnt->mnt_mounts); @@ -205,14 +254,19 @@ struct vfsmount *alloc_vfsmnt(const char #ifdef CONFIG_SMP mnt->mnt_writers = alloc_percpu(int); if (!mnt->mnt_writers) - goto out_free_devname; + goto out_free_mntcount; #else mnt->mnt_writers = 0; #endif + preempt_disable(); + inc_mnt_count(mnt); + preempt_enable(); } return mnt; #ifdef CONFIG_SMP +out_free_mntcount: + free_percpu(mnt->mnt_count); out_free_devname: kfree(mnt->mnt_devname); #endif @@ -526,9 +580,11 @@ static void detach_mnt(struct vfsmount * old_path->mnt = mnt->mnt_parent; mnt->mnt_parent = mnt; mnt->mnt_mountpoint = mnt->mnt_root; - list_del_init(&mnt->mnt_child); list_del_init(&mnt->mnt_hash); + list_del_init(&mnt->mnt_child); old_path->dentry->d_mounted--; + WARN_ON(mnt->mnt_mounted != 1); + mnt->mnt_mounted--; } void mnt_set_mountpoint(struct vfsmount *mnt, struct dentry *dentry, @@ -545,6 +601,8 @@ static void attach_mnt(struct vfsmount * list_add_tail(&mnt->mnt_hash, mount_hashtable + hash(path->mnt, path->dentry)); list_add_tail(&mnt->mnt_child, &path->mnt->mnt_mounts); + WARN_ON(mnt->mnt_mounted != 0); + mnt->mnt_mounted++; } /* @@ -567,6 +625,8 @@ static void commit_tree(struct vfsmount list_add_tail(&mnt->mnt_hash, mount_hashtable + hash(parent, mnt->mnt_mountpoint)); list_add_tail(&mnt->mnt_child, &parent->mnt_mounts); + WARN_ON(mnt->mnt_mounted != 0); + mnt->mnt_mounted++; touch_mnt_namespace(n); } @@ -670,50 +730,80 @@ static inline void __mntput(struct vfsmo void mntput_no_expire(struct vfsmount *mnt) { -repeat: - /* open-code atomic_dec_and_lock for the vfsmount lock */ - if (atomic_add_unless(&mnt->mnt_count, -1, 1)) + if (likely(mnt->mnt_mounted)) { + vfsmount_read_lock(); + if (unlikely(!mnt->mnt_mounted)) { + vfsmount_read_unlock(); + goto repeat; + } + dec_mnt_count(mnt); + BUG_ON(count_mnt_count(mnt) == 0); + vfsmount_read_unlock(); + return; + } + +repeat: vfsmount_write_lock(); - if (!atomic_dec_and_test(&mnt->mnt_count)) { + BUG_ON(mnt->mnt_mounted); + dec_mnt_count(mnt); + if (count_mnt_count(mnt)) { vfsmount_write_unlock(); return; } - if (likely(!mnt->mnt_pinned)) { vfsmount_write_unlock(); __mntput(mnt); return; } - atomic_add(mnt->mnt_pinned + 1, &mnt->mnt_count); + add_mnt_count(mnt, mnt->mnt_pinned + 1); mnt->mnt_pinned = 0; vfsmount_write_unlock(); acct_auto_close_mnt(mnt); security_sb_umount_close(mnt); goto repeat; } - EXPORT_SYMBOL(mntput_no_expire); +void mntput(struct vfsmount *mnt) +{ + if (mnt) { + /* avoid cacheline pingpong */ + if (unlikely(mnt->mnt_expiry_mark)) + mnt->mnt_expiry_mark = 0; + mntput_no_expire(mnt); + } +} +EXPORT_SYMBOL(mntput); + +struct vfsmount *mntget(struct vfsmount *mnt) +{ + if (mnt) { + preempt_disable(); + inc_mnt_count(mnt); + preempt_enable(); + } + return mnt; +} +EXPORT_SYMBOL(mntget); + void mnt_pin(struct vfsmount *mnt) { vfsmount_write_lock(); mnt->mnt_pinned++; vfsmount_write_unlock(); } - EXPORT_SYMBOL(mnt_pin); void mnt_unpin(struct vfsmount *mnt) { vfsmount_write_lock(); if (mnt->mnt_pinned) { - atomic_inc(&mnt->mnt_count); + inc_mnt_count(mnt); mnt->mnt_pinned--; } vfsmount_write_unlock(); } - EXPORT_SYMBOL(mnt_unpin); static inline void mangle(struct seq_file *m, const char *s) @@ -996,7 +1086,7 @@ int may_umount_tree(struct vfsmount *mnt vfsmount_read_lock(); for (p = mnt; p; p = next_mnt(p, mnt)) { - actual_refs += atomic_read(&p->mnt_count); + actual_refs += count_mnt_count(p); minimum_refs += 2; } vfsmount_read_unlock(); @@ -1076,6 +1166,8 @@ void umount_tree(struct vfsmount *mnt, i __touch_mnt_namespace(p->mnt_ns); p->mnt_ns = NULL; list_del_init(&p->mnt_child); + WARN_ON(p->mnt_mounted != 1); + p->mnt_mounted--; if (p->mnt_parent != p) { p->mnt_parent->mnt_ghosts++; p->mnt_mountpoint->d_mounted--; @@ -1107,7 +1199,7 @@ static int do_umount(struct vfsmount *mn flags & (MNT_FORCE | MNT_DETACH)) return -EINVAL; - if (atomic_read(&mnt->mnt_count) != 2) + if (count_mnt_count(mnt) != 2) return -EBUSY; if (!xchg(&mnt->mnt_expiry_mark, 1)) Index: linux-2.6/include/linux/mount.h =================================================================== --- linux-2.6.orig/include/linux/mount.h +++ linux-2.6/include/linux/mount.h @@ -56,20 +56,20 @@ struct vfsmount { struct mnt_namespace *mnt_ns; /* containing namespace */ int mnt_id; /* mount identifier */ int mnt_group_id; /* peer group identifier */ - /* - * We put mnt_count & mnt_expiry_mark at the end of struct vfsmount - * to let these frequently modified fields in a separate cache line - * (so that reads of mnt_flags wont ping-pong on SMP machines) - */ - atomic_t mnt_count; int mnt_expiry_mark; /* true if marked for expiry */ int mnt_pinned; int mnt_ghosts; + int mnt_mounted; #ifdef CONFIG_SMP int *mnt_writers; #else int mnt_writers; #endif +#ifdef CONFIG_SMP + int *mnt_count; +#else + int mnt_count; +#endif }; static inline int *get_mnt_writers_ptr(struct vfsmount *mnt) @@ -81,13 +81,6 @@ static inline int *get_mnt_writers_ptr(s #endif } -static inline struct vfsmount *mntget(struct vfsmount *mnt) -{ - if (mnt) - atomic_inc(&mnt->mnt_count); - return mnt; -} - struct file; /* forward dec */ extern void vfsmount_read_lock(void); @@ -95,23 +88,21 @@ extern void vfsmount_read_unlock(void); extern void vfsmount_write_lock(void); extern void vfsmount_write_unlock(void); +extern unsigned int count_mnt_count(struct vfsmount *mnt); + extern int mnt_want_write(struct vfsmount *mnt); extern int mnt_want_write_file(struct file *file); extern int mnt_clone_write(struct vfsmount *mnt); extern void mnt_drop_write(struct vfsmount *mnt); + extern void mntput_no_expire(struct vfsmount *mnt); +extern struct vfsmount *mntget(struct vfsmount *mnt); +extern void mntput(struct vfsmount *mnt); + extern void mnt_pin(struct vfsmount *mnt); extern void mnt_unpin(struct vfsmount *mnt); extern int __mnt_is_readonly(struct vfsmount *mnt); -static inline void mntput(struct vfsmount *mnt) -{ - if (mnt) { - mnt->mnt_expiry_mark = 0; - mntput_no_expire(mnt); - } -} - extern struct vfsmount *do_kern_mount(const char *fstype, int flags, const char *name, void *data); Index: linux-2.6/fs/pnode.c =================================================================== --- linux-2.6.orig/fs/pnode.c +++ linux-2.6/fs/pnode.c @@ -279,7 +279,7 @@ out: */ static inline int do_refcount_check(struct vfsmount *mnt, int count) { - int mycount = atomic_read(&mnt->mnt_count) - mnt->mnt_ghosts; + int mycount = count_mnt_count(mnt) - mnt->mnt_ghosts; return (mycount > count); } Index: linux-2.6/fs/libfs.c =================================================================== --- linux-2.6.orig/fs/libfs.c +++ linux-2.6/fs/libfs.c @@ -244,6 +244,7 @@ int get_sb_pseudo(struct file_system_typ d_instantiate(dentry, root); s->s_root = dentry; s->s_flags |= MS_ACTIVE; + mnt->mnt_mounted++; /* never unmounted, shortcut mntget (XXX: OK?) */ simple_set_mnt(mnt, s); return 0; -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html