[PATCH] inotify: lock avoidance with parent watch status in dentry
Previous inotify work avoidance is good when inotify is completely unused,
but it breaks down if even a single watch is in place anywhere in the
system. Robin Holt notices that udev is one such culprit - it slows down a
512-thread application on a 512 CPU system from 6 seconds to 22 minutes.
Solve this by adding a flag in the dentry that tells inotify whether or not
its parent inode has a watch on it. Event queueing to parent will skip
taking locks if this flag is cleared. Setting and clearing of this flag on
all child dentries versus event delivery: this is no in terms of race
cases, and that was shown to be equivalent to always performing the check.
The essential behaviour is that activity occuring _after_ a watch has been
added and _before_ it has been removed, will generate events.
Signed-off-by: Nick Piggin <npiggin@suse.de>
Cc: Robert Love <rml@novell.com>
Cc: John McCutchan <ttb@tentacle.dhs.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/fs/dcache.c b/fs/dcache.c
index 139e5fd..0f7ec12 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -802,6 +802,7 @@
if (inode)
list_add(&entry->d_alias, &inode->i_dentry);
entry->d_inode = inode;
+ fsnotify_d_instantiate(entry, inode);
spin_unlock(&dcache_lock);
security_d_instantiate(entry, inode);
}
@@ -853,6 +854,7 @@
list_add(&entry->d_alias, &inode->i_dentry);
do_negative:
entry->d_inode = inode;
+ fsnotify_d_instantiate(entry, inode);
spin_unlock(&dcache_lock);
security_d_instantiate(entry, inode);
return NULL;
@@ -983,6 +985,7 @@
new = __d_find_alias(inode, 1);
if (new) {
BUG_ON(!(new->d_flags & DCACHE_DISCONNECTED));
+ fsnotify_d_instantiate(new, inode);
spin_unlock(&dcache_lock);
security_d_instantiate(new, inode);
d_rehash(dentry);
@@ -992,6 +995,7 @@
/* d_instantiate takes dcache_lock, so we do it by hand */
list_add(&dentry->d_alias, &inode->i_dentry);
dentry->d_inode = inode;
+ fsnotify_d_instantiate(dentry, inode);
spin_unlock(&dcache_lock);
security_d_instantiate(dentry, inode);
d_rehash(dentry);
@@ -1176,6 +1180,9 @@
spin_lock(&dentry->d_lock);
isdir = S_ISDIR(dentry->d_inode->i_mode);
if (atomic_read(&dentry->d_count) == 1) {
+ /* remove this and other inotify debug checks after 2.6.18 */
+ dentry->d_flags &= ~DCACHE_INOTIFY_PARENT_WATCHED;
+
dentry_iput(dentry);
fsnotify_nameremove(dentry, isdir);
return;
@@ -1342,6 +1349,7 @@
list_add(&dentry->d_u.d_child, &dentry->d_parent->d_subdirs);
spin_unlock(&target->d_lock);
+ fsnotify_d_move(dentry);
spin_unlock(&dentry->d_lock);
write_sequnlock(&rename_lock);
spin_unlock(&dcache_lock);
diff --git a/fs/inotify.c b/fs/inotify.c
index 0ee39ef..a61e93e 100644
--- a/fs/inotify.c
+++ b/fs/inotify.c
@@ -38,7 +38,6 @@
#include <asm/ioctls.h>
static atomic_t inotify_cookie;
-static atomic_t inotify_watches;
static kmem_cache_t *watch_cachep;
static kmem_cache_t *event_cachep;
@@ -381,6 +380,48 @@
}
/*
+ * inotify_inode_watched - returns nonzero if there are watches on this inode
+ * and zero otherwise. We call this lockless, we do not care if we race.
+ */
+static inline int inotify_inode_watched(struct inode *inode)
+{
+ return !list_empty(&inode->inotify_watches);
+}
+
+/*
+ * Get child dentry flag into synch with parent inode.
+ * Flag should always be clear for negative dentrys.
+ */
+static void set_dentry_child_flags(struct inode *inode, int watched)
+{
+ struct dentry *alias;
+
+ spin_lock(&dcache_lock);
+ list_for_each_entry(alias, &inode->i_dentry, d_alias) {
+ struct dentry *child;
+
+ list_for_each_entry(child, &alias->d_subdirs, d_u.d_child) {
+ if (!child->d_inode) {
+ WARN_ON(child->d_flags & DCACHE_INOTIFY_PARENT_WATCHED);
+ continue;
+ }
+ spin_lock(&child->d_lock);
+ if (watched) {
+ WARN_ON(child->d_flags &
+ DCACHE_INOTIFY_PARENT_WATCHED);
+ child->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;
+ } else {
+ WARN_ON(!(child->d_flags &
+ DCACHE_INOTIFY_PARENT_WATCHED));
+ child->d_flags&=~DCACHE_INOTIFY_PARENT_WATCHED;
+ }
+ spin_unlock(&child->d_lock);
+ }
+ }
+ spin_unlock(&dcache_lock);
+}
+
+/*
* create_watch - creates a watch on the given device.
*
* Callers must hold dev->mutex. Calls inotify_dev_get_wd() so may sleep.
@@ -426,7 +467,6 @@
get_inotify_watch(watch);
atomic_inc(&dev->user->inotify_watches);
- atomic_inc(&inotify_watches);
return watch;
}
@@ -458,8 +498,10 @@
list_del(&watch->i_list);
list_del(&watch->d_list);
+ if (!inotify_inode_watched(watch->inode))
+ set_dentry_child_flags(watch->inode, 0);
+
atomic_dec(&dev->user->inotify_watches);
- atomic_dec(&inotify_watches);
idr_remove(&dev->idr, watch->wd);
put_inotify_watch(watch);
}
@@ -481,16 +523,39 @@
remove_watch_no_event(watch, dev);
}
+/* Kernel API */
+
/*
- * inotify_inode_watched - returns nonzero if there are watches on this inode
- * and zero otherwise. We call this lockless, we do not care if we race.
+ * inotify_d_instantiate - instantiate dcache entry for inode
*/
-static inline int inotify_inode_watched(struct inode *inode)
+void inotify_d_instantiate(struct dentry *entry, struct inode *inode)
{
- return !list_empty(&inode->inotify_watches);
+ struct dentry *parent;
+
+ if (!inode)
+ return;
+
+ WARN_ON(entry->d_flags & DCACHE_INOTIFY_PARENT_WATCHED);
+ spin_lock(&entry->d_lock);
+ parent = entry->d_parent;
+ if (inotify_inode_watched(parent->d_inode))
+ entry->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;
+ spin_unlock(&entry->d_lock);
}
-/* Kernel API */
+/*
+ * inotify_d_move - dcache entry has been moved
+ */
+void inotify_d_move(struct dentry *entry)
+{
+ struct dentry *parent;
+
+ parent = entry->d_parent;
+ if (inotify_inode_watched(parent->d_inode))
+ entry->d_flags |= DCACHE_INOTIFY_PARENT_WATCHED;
+ else
+ entry->d_flags &= ~DCACHE_INOTIFY_PARENT_WATCHED;
+}
/**
* inotify_inode_queue_event - queue an event to all watches on this inode
@@ -538,7 +603,7 @@
struct dentry *parent;
struct inode *inode;
- if (!atomic_read (&inotify_watches))
+ if (!(dentry->d_flags & DCACHE_INOTIFY_PARENT_WATCHED))
return;
spin_lock(&dentry->d_lock);
@@ -993,6 +1058,9 @@
goto out;
}
+ if (!inotify_inode_watched(inode))
+ set_dentry_child_flags(inode, 1);
+
/* Add the watch to the device's and the inode's list */
list_add(&watch->d_list, &dev->watches);
list_add(&watch->i_list, &inode->inotify_watches);
@@ -1065,7 +1133,6 @@
inotify_max_user_watches = 8192;
atomic_set(&inotify_cookie, 0);
- atomic_set(&inotify_watches, 0);
watch_cachep = kmem_cache_create("inotify_watch_cache",
sizeof(struct inotify_watch),
