Commit 7012b02a authored by Jeff Layton's avatar Jeff Layton Committed by Al Viro

locks: move file_lock_list to a set of percpu hlist_heads and convert file_lock_lock to an lglock

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: default avatarJeff Layton <jlayton@redhat.com>
Acked-by: default avatarJ. Bruce Fields <bfields@fieldses.org>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 0bc77381
......@@ -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;
}
......
......@@ -954,6 +954,7 @@ 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;
......
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