The file_lock_list is only used for /proc/locks. The vastly common case
is for locks to be put onto the list and come off again, without ever
being traversed.
Help optimize for this use-case by moving to percpu hlist_head-s. At the
same time, we can make the locking less contentious by moving to an
lglock. When iterating over the lists for /proc/locks, we must take the
global lock and then iterate over each CPU's list in turn.
This change necessitates a new fl_link_cpu field to keep track of which
CPU the entry is on. On x86_64 at least, this field is placed within an
existing hole in the struct to avoid growing the size.
Signed-off-by: Jeff Layton <jlayton@xxxxxxxxxx>
Acked-by: J. Bruce Fields <bfields@xxxxxxxxxxxx>
---
fs/locks.c | 69 +++++++++++++++++++++++++++++++++++++---------------
include/linux/fs.h | 1 +
2 files changed, 50 insertions(+), 20 deletions(-)
diff --git a/fs/locks.c b/fs/locks.c
index 04e2c1f..0f544cd 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -127,6 +127,8 @@
#include <linux/rcupdate.h>
#include <linux/pid_namespace.h>
#include <linux/hashtable.h>
+#include <linux/percpu.h>
+#include <linux/lglock.h>
#include <asm/uaccess.h>
@@ -155,11 +157,13 @@ int lease_break_time = 45;
for (lockp = &inode->i_flock; *lockp != NULL; lockp = &(*lockp)->fl_next)
/*
- * The global file_lock_list is only used for displaying /proc/locks. Protected
- * by the file_lock_lock.
+ * The global file_lock_list is only used for displaying /proc/locks, so we
+ * keep a list on each CPU, with each list protected by its own spinlock via
+ * the file_lock_lglock. Note that alterations to the list also require that
+ * the relevant i_lock is held.
*/
-static HLIST_HEAD(file_lock_list);
-static DEFINE_SPINLOCK(file_lock_lock);
+DEFINE_STATIC_LGLOCK(file_lock_lglock);
+static DEFINE_PER_CPU(struct hlist_head, file_lock_list);
/*
* The blocked_hash is used to find POSIX lock loops for deadlock detection.
@@ -506,20 +510,30 @@ static int posix_same_owner(struct file_lock *fl1, struct file_lock *fl2)
return fl1->fl_owner == fl2->fl_owner;
}
+/* Must be called with the i_lock held! */
static inline void
locks_insert_global_locks(struct file_lock *fl)
{
- spin_lock(&file_lock_lock);
- hlist_add_head(&fl->fl_link, &file_lock_list);
- spin_unlock(&file_lock_lock);
+ lg_local_lock(&file_lock_lglock);
+ fl->fl_link_cpu = smp_processor_id();
+ hlist_add_head(&fl->fl_link, this_cpu_ptr(&file_lock_list));
+ lg_local_unlock(&file_lock_lglock);
}
+/* Must be called with the i_lock held! */
static inline void
locks_delete_global_locks(struct file_lock *fl)
{
- spin_lock(&file_lock_lock);
+ /*
+ * Avoid taking lock if already unhashed. This is safe since this check
+ * is done while holding the i_lock, and new insertions into the list
+ * also require that it be held.
+ */
+ if (hlist_unhashed(&fl->fl_link))
+ return;
+ lg_local_lock_cpu(&file_lock_lglock, fl->fl_link_cpu);
hlist_del_init(&fl->fl_link);
- spin_unlock(&file_lock_lock);
+ lg_local_unlock_cpu(&file_lock_lglock, fl->fl_link_cpu);
}
static unsigned long
@@ -2243,6 +2257,11 @@ EXPORT_SYMBOL_GPL(vfs_cancel_lock);
#include <linux/proc_fs.h>
#include <linux/seq_file.h>
+struct locks_iterator {
+ int li_cpu;
+ loff_t li_pos;
+};
+
static void lock_get_status(struct seq_file *f, struct file_lock *fl,
loff_t id, char *pfx)
{
@@ -2316,39 +2335,41 @@ static void lock_get_status(struct seq_file *f, struct file_lock *fl,
static int locks_show(struct seq_file *f, void *v)
{
+ struct locks_iterator *iter = f->private;
struct file_lock *fl, *bfl;
fl = hlist_entry(v, struct file_lock, fl_link);
- lock_get_status(f, fl, *((loff_t *)f->private), "");
+ lock_get_status(f, fl, iter->li_pos, "");
list_for_each_entry(bfl, &fl->fl_block, fl_block)
- lock_get_status(f, bfl, *((loff_t *)f->private), " ->");
+ lock_get_status(f, bfl, iter->li_pos, " ->");
return 0;
}
static void *locks_start(struct seq_file *f, loff_t *pos)
{
- loff_t *p = f->private;
+ struct locks_iterator *iter = f->private;
- spin_lock(&file_lock_lock);
+ iter->li_pos = *pos + 1;
+ lg_global_lock(&file_lock_lglock);
spin_lock(&blocked_lock_lock);
- *p = (*pos + 1);
- return seq_hlist_start(&file_lock_list, *pos);
+ return seq_hlist_start_percpu(&file_lock_list, &iter->li_cpu, *pos);
}
static void *locks_next(struct seq_file *f, void *v, loff_t *pos)
{
- loff_t *p = f->private;
- ++*p;
- return seq_hlist_next(v, &file_lock_list, pos);
+ struct locks_iterator *iter = f->private;
+
+ ++iter->li_pos;
+ return seq_hlist_next_percpu(v, &file_lock_list, &iter->li_cpu, pos);
}
static void locks_stop(struct seq_file *f, void *v)
{
spin_unlock(&blocked_lock_lock);
- spin_unlock(&file_lock_lock);
+ lg_global_unlock(&file_lock_lglock);
}
static const struct seq_operations locks_seq_operations = {
@@ -2360,7 +2381,8 @@ static const struct seq_operations locks_seq_operations = {
static int locks_open(struct inode *inode, struct file *filp)
{
- return seq_open_private(filp, &locks_seq_operations, sizeof(loff_t));
+ return seq_open_private(filp, &locks_seq_operations,
+ sizeof(struct locks_iterator));
}
static const struct file_operations proc_locks_operations = {
@@ -2460,9 +2482,16 @@ EXPORT_SYMBOL(lock_may_write);
static int __init filelock_init(void)
{
+ int i;
+
filelock_cache = kmem_cache_create("file_lock_cache",
sizeof(struct file_lock), 0, SLAB_PANIC, NULL);
+ lg_lock_init(&file_lock_lglock, "file_lock_lglock");
+
+ for_each_possible_cpu(i)
+ INIT_HLIST_HEAD(per_cpu_ptr(&file_lock_list, i));
+
return 0;
}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e42e04f..039f2ae 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -953,6 +953,7 @@ struct file_lock {
unsigned int fl_flags;
unsigned char fl_type;
unsigned int fl_pid;
+ int fl_link_cpu; /* what cpu's list is this on? */
struct pid *fl_nspid;
wait_queue_head_t fl_wait;
struct file *fl_file;
--
1.7.1
--
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