From fa0d7e3de6d6fc5004ad9dea0dd6b286af8f03e9 Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Fri, 7 Jan 2011 17:49:49 +1100 Subject: fs: icache RCU free inodes RCU free the struct inode. This will allow: - Subsequent store-free path walking patch. The inode must be consulted for permissions when walking, so an RCU inode reference is a must. - sb_inode_list_lock to be moved inside i_lock because sb list walkers who want to take i_lock no longer need to take sb_inode_list_lock to walk the list in the first place. This will simplify and optimize locking. - Could remove some nested trylock loops in dcache code - Could potentially simplify things a bit in VM land. Do not need to take the page lock to follow page->mapping. The downsides of this is the performance cost of using RCU. In a simple creat/unlink microbenchmark, performance drops by about 10% due to inability to reuse cache-hot slab objects. As iterations increase and RCU freeing starts kicking over, this increases to about 20%. In cases where inode lifetimes are longer (ie. many inodes may be allocated during the average life span of a single inode), a lot of this cache reuse is not applicable, so the regression caused by this patch is smaller. The cache-hot regression could largely be avoided by using SLAB_DESTROY_BY_RCU, however this adds some complexity to list walking and store-free path walking, so I prefer to implement this at a later date, if it is shown to be a win in real situations. I haven't found a regression in any non-micro benchmark so I doubt it will be a problem. Signed-off-by: Nick Piggin --- net/socket.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) (limited to 'net/socket.c') diff --git a/net/socket.c b/net/socket.c index 088fb3fd45e..97fff3a4e72 100644 --- a/net/socket.c +++ b/net/socket.c @@ -262,20 +262,20 @@ static struct inode *sock_alloc_inode(struct super_block *sb) } -static void wq_free_rcu(struct rcu_head *head) +static void sock_free_rcu(struct rcu_head *head) { - struct socket_wq *wq = container_of(head, struct socket_wq, rcu); + struct inode *inode = container_of(head, struct inode, i_rcu); + struct socket_alloc *ei = container_of(inode, struct socket_alloc, + vfs_inode); - kfree(wq); + kfree(ei->socket.wq); + INIT_LIST_HEAD(&inode->i_dentry); + kmem_cache_free(sock_inode_cachep, ei); } static void sock_destroy_inode(struct inode *inode) { - struct socket_alloc *ei; - - ei = container_of(inode, struct socket_alloc, vfs_inode); - call_rcu(&ei->socket.wq->rcu, wq_free_rcu); - kmem_cache_free(sock_inode_cachep, ei); + call_rcu(&inode->i_rcu, sock_free_rcu); } static void init_once(void *foo) -- cgit v1.2.3 From ff0c7d15f9787b7e8c601533c015295cc68329f8 Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Fri, 7 Jan 2011 17:49:50 +1100 Subject: fs: avoid inode RCU freeing for pseudo fs Pseudo filesystems that don't put inode on RCU list or reachable by rcu-walk dentries do not need to RCU free their inodes. Signed-off-by: Nick Piggin --- net/socket.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) (limited to 'net/socket.c') diff --git a/net/socket.c b/net/socket.c index 97fff3a4e72..817dc92e9ef 100644 --- a/net/socket.c +++ b/net/socket.c @@ -262,20 +262,21 @@ static struct inode *sock_alloc_inode(struct super_block *sb) } -static void sock_free_rcu(struct rcu_head *head) + +static void wq_free_rcu(struct rcu_head *head) { - struct inode *inode = container_of(head, struct inode, i_rcu); - struct socket_alloc *ei = container_of(inode, struct socket_alloc, - vfs_inode); + struct socket_wq *wq = container_of(head, struct socket_wq, rcu); - kfree(ei->socket.wq); - INIT_LIST_HEAD(&inode->i_dentry); - kmem_cache_free(sock_inode_cachep, ei); + kfree(wq); } static void sock_destroy_inode(struct inode *inode) { - call_rcu(&inode->i_rcu, sock_free_rcu); + struct socket_alloc *ei; + + ei = container_of(inode, struct socket_alloc, vfs_inode); + call_rcu(&ei->socket.wq->rcu, wq_free_rcu); + kmem_cache_free(sock_inode_cachep, ei); } static void init_once(void *foo) -- cgit v1.2.3 From fb045adb99d9b7c562dc7fef834857f78249daa1 Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Fri, 7 Jan 2011 17:49:55 +1100 Subject: fs: dcache reduce branches in lookup path Reduce some branches and memory accesses in dcache lookup by adding dentry flags to indicate common d_ops are set, rather than having to check them. This saves a pointer memory access (dentry->d_op) in common path lookup situations, and saves another pointer load and branch in cases where we have d_op but not the particular operation. Patched with: git grep -E '[.>]([[:space:]])*d_op([[:space:]])*=' | xargs sed -e 's/\([^\t ]*\)->d_op = \(.*\);/d_set_d_op(\1, \2);/' -e 's/\([^\t ]*\)\.d_op = \(.*\);/d_set_d_op(\&\1, \2);/' -i Signed-off-by: Nick Piggin --- net/socket.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'net/socket.c') diff --git a/net/socket.c b/net/socket.c index 817dc92e9ef..991e266bc7a 100644 --- a/net/socket.c +++ b/net/socket.c @@ -368,7 +368,7 @@ static int sock_alloc_file(struct socket *sock, struct file **f, int flags) } path.mnt = mntget(sock_mnt); - path.dentry->d_op = &sockfs_dentry_operations; + d_set_d_op(path.dentry, &sockfs_dentry_operations); d_instantiate(path.dentry, SOCK_INODE(sock)); SOCK_INODE(sock)->i_fop = &socket_file_ops; -- cgit v1.2.3 From 4b936885ab04dc6e0bb0ef35e0e23c1a7364d9e5 Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Fri, 7 Jan 2011 17:50:07 +1100 Subject: fs: improve scalability of pseudo filesystems Regardless of how much we possibly try to scale dcache, there is likely always going to be some fundamental contention when adding or removing children under the same parent. Pseudo filesystems do not seem need to have connected dentries because by definition they are disconnected. Signed-off-by: Nick Piggin --- net/socket.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'net/socket.c') diff --git a/net/socket.c b/net/socket.c index 991e266bc7a..0ee74c32532 100644 --- a/net/socket.c +++ b/net/socket.c @@ -361,7 +361,7 @@ static int sock_alloc_file(struct socket *sock, struct file **f, int flags) if (unlikely(fd < 0)) return fd; - path.dentry = d_alloc(sock_mnt->mnt_sb->s_root, &name); + path.dentry = d_alloc_pseudo(sock_mnt->mnt_sb, &name); if (unlikely(!path.dentry)) { put_unused_fd(fd); return -ENOMEM; -- cgit v1.2.3 From b3e19d924b6eaf2ca7d22cba99a517c5171007b6 Mon Sep 17 00:00:00 2001 From: Nick Piggin Date: Fri, 7 Jan 2011 17:50:11 +1100 Subject: fs: scale mntget/mntput The problem that this patch aims to fix is vfsmount refcounting scalability. We need to take a reference on the vfsmount for every successful path lookup, which often go to the same mount point. The fundamental difficulty is that a "simple" reference count can never be made scalable, because any time a reference is dropped, we must check whether that was the last reference. To do that requires communication with all other CPUs that may have taken a reference count. We can make refcounts more scalable in a couple of ways, involving keeping distributed counters, and checking for the global-zero condition less frequently. - check the global sum once every interval (this will delay zero detection for some interval, so it's probably a showstopper for vfsmounts). - keep a local count and only taking the global sum when local reaches 0 (this is difficult for vfsmounts, because we can't hold preempt off for the life of a reference, so a counter would need to be per-thread or tied strongly to a particular CPU which requires more locking). - keep a local difference of increments and decrements, which allows us to sum the total difference and hence find the refcount when summing all CPUs. Then, keep a single integer "long" refcount for slow and long lasting references, and only take the global sum of local counters when the long refcount is 0. This last scheme is what I implemented here. Attached mounts and process root and working directory references are "long" references, and everything else is a short reference. This allows scalable vfsmount references during path walking over mounted subtrees and unattached (lazy umounted) mounts with processes still running in them. This results in one fewer atomic op in the fastpath: mntget is now just a per-CPU inc, rather than an atomic inc; and mntput just requires a spinlock and non-atomic decrement in the common case. However code is otherwise bigger and heavier, so single threaded performance is basically a wash. Signed-off-by: Nick Piggin --- net/socket.c | 19 +++++++++++++++++-- 1 file changed, 17 insertions(+), 2 deletions(-) (limited to 'net/socket.c') diff --git a/net/socket.c b/net/socket.c index 0ee74c32532..815bba3d2fe 100644 --- a/net/socket.c +++ b/net/socket.c @@ -2390,6 +2390,8 @@ EXPORT_SYMBOL(sock_unregister); static int __init sock_init(void) { + int err; + /* * Initialize sock SLAB cache. */ @@ -2406,8 +2408,15 @@ static int __init sock_init(void) */ init_inodecache(); - register_filesystem(&sock_fs_type); + + err = register_filesystem(&sock_fs_type); + if (err) + goto out_fs; sock_mnt = kern_mount(&sock_fs_type); + if (IS_ERR(sock_mnt)) { + err = PTR_ERR(sock_mnt); + goto out_mount; + } /* The real protocol initialization is performed in later initcalls. */ @@ -2420,7 +2429,13 @@ static int __init sock_init(void) skb_timestamping_init(); #endif - return 0; +out: + return err; + +out_mount: + unregister_filesystem(&sock_fs_type); +out_fs: + goto out; } core_initcall(sock_init); /* early initcall */ -- cgit v1.2.3