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 --- fs/anon_inodes.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fs/anon_inodes.c') diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c index 57ce55b..aca8806 100644 --- a/fs/anon_inodes.c +++ b/fs/anon_inodes.c @@ -113,7 +113,7 @@ struct file *anon_inode_getfile(const char *name, */ ihold(anon_inode_inode); - path.dentry->d_op = &anon_inodefs_dentry_operations; + d_set_d_op(path.dentry, &anon_inodefs_dentry_operations); d_instantiate(path.dentry, anon_inode_inode); error = -ENFILE; -- cgit v1.1 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 --- fs/anon_inodes.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fs/anon_inodes.c') diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c index aca8806..9d92b33 100644 --- a/fs/anon_inodes.c +++ b/fs/anon_inodes.c @@ -102,7 +102,7 @@ struct file *anon_inode_getfile(const char *name, this.name = name; this.len = strlen(name); this.hash = 0; - path.dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this); + path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this); if (!path.dentry) goto err_module; -- cgit v1.1 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 --- fs/anon_inodes.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fs/anon_inodes.c') diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c index 9d92b33..5fd38112a 100644 --- a/fs/anon_inodes.c +++ b/fs/anon_inodes.c @@ -232,7 +232,7 @@ static int __init anon_inode_init(void) return 0; err_mntput: - mntput(anon_inode_mnt); + mntput_long(anon_inode_mnt); err_unregister_filesystem: unregister_filesystem(&anon_inode_fs_type); err_exit: -- cgit v1.1